Analysis of the rainwater harvesting system contribution toward the universalization of urban water access under the water utility perspective

Uma análise da contribuição de sistemas de aproveitamento de águas chuva para a universalização do acesso à água em ambientes urbanos: uma perspectiva da companhia de saneamento

ABSTRACT

The Brazilian New Legal Sanitation Framework approved in July 2020 included the Rainwater Harvesting Systems (RHS) as strategic alternative to reach universal urban water access in the country. Despite the vast literature on assessing the RWHS´s viability for households and establishments, there is lack of understanding on the impacts of the dissemination of this initiative to water utilities. This work proposed and applied a methodology to evaluate the impact of RHS dissemination on the performance of water utilities in the Federal District of Brazil. The methodology consisted of computing the potential water saving based on water balance of the RHS for non-potable water demand, selecting and evaluating operational and economic indicators of the water utility performance and computing economic evaluation of different scenarios of RHS dissemination. Results demonstrated that in most of the scenarios, the dissemination of RHS is not favorable to the water utility in terms of financial balance, mostly due to the loss of revenue given the reduction of water volume consumption. However, the financial balance has been extended to incorporate the possible sale of the saved water volume to categories of consumers with higher willingness to pay, such as, commercial, industrial or public users. Additional consideration of environmental benefits of RHS and other sale opportunities could also benefit the overall economic analysis of RHS as a public policy.

Keywords:
Decentralized sanitation; Urban water resources management; Economic evaluation

RESUMO

Sistemas de aproveitamento de água de chuva (SAAC) foram incluídos no Novo Marco Legal do Saneamento aprovado em julho de 2020 como alternativa estratégica para o alcance do acesso universal a água. Apesar da vasta literatura em avaliação de viabilidade de SAAC para residências e estabelecimentos, pouco tem sido analisado sobre os impactos da ampla disseminação desses sistemas para as companhias de saneamento. O presente trabalho propôs e aplicou metodologia para avaliar o impacto da disseminação de SAAC na perspectiva da companhia de saneamento na região do Distrito Federal do Brasil. A metodologia consistiu em calcular o potencial de aproveitamento de água de chuva por meio de simulação de balanço hídrico para atender demanda não potável de água em cenários diferentes de residências; seleção e avaliação de indicadores operacionais e econômicos de desempenho da companhia de saneamento e consideração de diferentes cenários de adesão ao SAAC. Resultados demonstraram que em muitos cenários a disseminação de SAAC não é favorável às companhias de saneamento em termos financeiros, principalmente em função da perda de receita resultante da redução do volume de água consumido. Mas foi possível demonstrar a melhoria da análise custo benefício para a companhia considerando a venda do volume economizado para usuários de outras categorias, tais como comercial, industrial e público que possuem tarifas mais altas. Sugere-se que fatores ambientais também sejam incluídos na análise econômica para melhor representar os benefícios da implantação de SAAC em larga escala.

Palavras-chave:
Saneamento descentralizado; Gestão de recursos hídricos urbanos; Avaliação econômica

INTRODUCTION

The universalization of water supply comes up against the growing increase in water demand. The potable water consumption in the world increased six times in the last century and continue to advance at 1% yearly, as a result of population growth, economic development and the increase in consumption (United Nations Educational, Scientific and Cultural Organization, 2021).

According to Romano et al. (2016) the search for rational alternatives of water supply involves adequate public policies (water tariffs, conservative consumption programs, reduction of water loss), demographic factors (population, income, social traditions) and climate conditions.

Among sustainable alternatives of water supply, the use of rainwater harvesting systems (RHS) integrated to traditional water supply systems has been considered a feasible solution for the goal of universal access to water in many communities (Maqsoom et al., 2021; United Nations Water, 2011; Lepcha et al., 2024; Wartalska et al., 2024). Sant’Ana et al. (2017) and Toosi et al. (2020) evaluated in different studies that the use of RHS and reuse of grey water as complementary systems of water supply is a promising alternative of green infrastructure capable to cover part of the urban water demand and to reduce the stress on water resources systems and respective water conflicts. They emphasized that the economic saving due to water conservation programs could create opportunities for new water tariff structures that could benefit the whole community.

Teston et al. (2018) verified that in many categories of buildings in Brazil (schools, commercial and public institutions) the non-potable use of water is the greatest amount of water consumption representing an opportunity to water conservation programs including the use of RHS and greywater reuse.

Many studies list the benefits of RHS for communities and the environment, such as reducing the stress over traditional water supply, reducing water pollution in urban rivers, reducing the risks of floods in highly impervious urban areas (Takagi et al., 2018; Stewart et al., 2019; Dijk et al., 2020; Prenner et al., 2021; Bertuzzi & Ghisi, 2021; NC Cooperative Extension, 2022; Teston et al., 2024). The advantages of RHS to individuals have also been highlighted in specific conditions especially when considering the substitution of non-potable uses (Li et al., 2010; Vialle et al., 2015; Stewart et al., 2019).

The environmental analysis of the value of RHS to societies has been pointed out by Vialle et al. (2015) stating that when all environmental benefits are correctly considered in the analysis, these systems may contribute to the Sustainable Development Goals (SDG) 6, SDG 11 and SDG 13, Universal Access to Clean Water and Sanitation, Sustainable Cities and Communities and Climate Actions, respectively.

The dissemination of RHS in Brazil has been driven by social and environmental aspects especially in rural areas where there are no traditional water supply systems and the communities are spatially dispersed or when the traditional systems are not reliable. Many municipalities have created legislation to regulate the use of RHS integrated to traditional water supply systems (Campisano & Lupia, 2017; Ward et al., 2019). Other work in Brazil also verified the viability of RHS considering different rainfall patterns, demand, rooftop surface areas and reservoirs’ capacities to accumulate the rainwater (Pacheco & Alves, 2023; Borgert & Ghisi, 2024; Pacheco, 2023).

Some of these regulations include RHS as an enforcement in cases of new households or buildings, others require the use of RHS when the roof area indicates viability. In many cases, the regulation includes other water conservation measures such as the use of water saving equipment, micro metering and water loss reduction (Ward et al., 2019).

The New Water and Sanitation Regulation (NWSR) stated in the Federal Law nº 14.026 from July, 15^th 2020 also emphasized the use of RHS and its benefits to urban drainage and to urban water supply (Brasil, 2020a). Seventeen states in Brazil and the Federal District of Brazil also have legislation that motivates the use of RHS in their water saving programs (Costa et al., 2021). However, there is still a lack of knowledge regarding the impacts of these regulations to the water utilities, considering both the benefits and the possible costs that are involved in the dissemination of RHS.

On the side of the water utilities, one could also list many contributions of the RHS when considered as a public policy. Some of these benefits are the postponing of new investments on additional infrastructures, improving the environmental image of the water utilities, operational cost reduction (chemicals, energy and network maintenance) and opportunities to reach other consumers (expanding the water supply system). Although these arguments are frequently listed, there is a lack of understanding on how these benefits relate to the costs involved in the overall use of RHS in a community, considering the perspective of the water utilities. There is also a gap in methodologies to analyze and quantify the relationship between benefits and costs to water utilities of implementing RHS to consumers.

For the dissemination of RHS it is crucial to understand the reduction in water consumption from traditional sources and its impacts on the costs and revenues of a water utility. This includes assessing whether the reduction is constant, for all households and evaluating its effects on operation and feasibility of the utilities. For this evaluation it is necessary to invest in studies that develop methods to quantify the impacts of RHS implementation to water utilities. The present research proposed a methodology to evaluate the influence of RHS public policies in cost benefit analysis as an effort to extend the RHS assessment considering both household and water utility perspectives.

MATERIAL AND METHODS

Figure 1 presents the general steps of the methodology to evaluate the impact of RHS for the water utility performance.

Figure 1
Graphical representation of the research methodology.

Characterization of the study area

The proposed methodology was applied to the Brazlandia Administrative Region (BAR) in the Federal District of Brazil.

Description of the BAR study area

The Brazlandia Administrative Region is a typical urban area in the Federal District of Brazil but has the particular characteristic that its water supply system is not connected to other Administrative Regions and has a separate water treatment plant.

The water supply system in the Federal District of Brazil is comprised of five water supply subsystems: Descoberto, Torto-Santa Maria, Sobradinho-Planaltina, São Sebastião and the Brazlandia subsystem. Recently, the Corumba Water Supply subsystem was added to the whole system in order to reduce the stress over the Descoberto subsystem.

The BAR is divided into five urban areas comprising of residential, commercial, and public institutional areas. The following areas are:

• Traditional area (where is the political and administrative buildings);

• Norte (residential and commercial);

• Sul (residential);

• Veredas (residential and commercial);

• Vila São José (residential).

Population and water demand in Brazlandia/FD

The urban population in Brazlandia was estimated in 2021 in 55,879 inhabitants, where 51.6% are women. According to Companhia de Planejamento do Distrito Federal (2021) 87.2% of households have ceramic roof tops and 99% of them are connected to the water utility CAESB. However, the Federal District household research in 2018 demonstrated that 37.7% of the households present some initiative, even preliminary, related to rainwater harvesting operating as an alternative source to provide water additional to the traditional systems from CAESB (Companhia de Planejamento do Distrito Federal, 2018).

Household characteristics in Brazlandia/FD

The sizes of the land parcel in Brazlandia were investigated using the Registered Parcels layer from the GeoPortal/FD information system. The average land parcel size for each neighborhood was computed and is shown in Table 1.

Table 1
Number of households, average size of land parcels and average surface area of roof top in Brazlandia’s neighborhoods.

Residential area	Number of households	Average parcel area (m2)	Average roof top surface area (m2)
				São José	5,663	169.49	108.22
Veredas	1,713	143.62	110.16
Tradicional	837	444.21	153.65
Norte	2,605	184.96	135.51
Sul	675	185.13	136.29

• Source: Geoportal/FD (Distrito Federal 2021).

Income data in Brazlandia/FD

The neighborhoods in Brazlandia were classified as in Sant’Ana et al. (2017) for different levels of income. The Vila São José and Veredas residential area were classified as lower income, while the other areas received the classification as slight lower.

Water consumption data and RHS in residential areas of Brazlandia/FD

The Rainwater harvesting potential was evaluated using the RHS water balance simulation in five residential areas of Brazlandia. The total water consumption in each residential area was computed according to the average water consumption and number of system connections of each water consumption interval of the tariff structure in September of 2019 (Companhia de Saneamento Ambiental do Distrito Federal, 2022) as illustrated in Table 2.

Table 2
Average water consumption, number of system connections and roof top surface area in each water consumption interval of residential areas in Brazlandia.

		Water Consumption Interval
		0 to 7 m3	8 to 13 m3	14 to 20 m3	21 to 30 m3	31 to 45 m3
Vila São José	Roof area (m2)	90	90	108	108	108
	Household connections	5	2,071	1,726	167	23
	Average consumption (m3/month)	4	11	16	23	33
Veredas	Roof area (m2)		90	110
	Household connections		703	626
	Average consumption (m3/month)		12	16
Tradicional	Roof area (m2)	90	90	153	153
	Household connections	1	78	425	31
	Average consumption (m3/month)	7	12	17	27
Norte	Roof area (m2)	90	90	135	135
	Household connections	35	653	1438	23
	Average consumption (m3/month)	4	11	16	23
Sul	Roof area (m2)		90	136
	Household connections		58	512
	Average consumption (m3/month)		11	16

• Source: Companhia de Saneamento Ambiental do Distrito Federal (2022) and GeoPortal/FD (Distrito Federal, 2021).

Using the data in Table 2, we computed the rainwater harvesting potential in volume based in Pacheco & Alves (2023) and Sant’Ana et al. (2017). The simulation considered five reservoirs’ capacities to accumulate the rainwater (0.5 m³, 1 m³, 5 m³, 10 m³ and 15 m³) and a daily precipitation series from rainfall gauge station 01548007 of the National Water and Sanitation Agency (ANA) from 01/10/1992 to 30/09/2022.

Building RHS Public Policies (RHSPP)

On the scope of the present work, the rainwater harvesting system is analyzed as an alternative of public policy toward the universalization of water and sanitation access. Considering the current knowledge about constraints and risks associated to the use of RHS in potable uses, we decided to limit the application of RHS to non-potable uses that require simple water treatment techniques. Frequent non-potable uses in households are gardening (lawn irrigation), vehicle washing, floor cleaning, toilet flushes and laundry. We named the three previous items as external uses (Ext) and defined the RHS demand as non-potable demands according to the following percentage of total water consumption in the household (Sant’Ana, 2011):

• External demand (Ext): 13% of the total household water demand originates in non-potable uses outside the house such as gardening, vehicle washing and floor cleaning.

• External demand and toilet (Ext & Tf): 28% of the total household water demand considering gardening, vehicle washing, floor cleaning and toilet flushes.

The RHSPP are defined in the present study as a government initiative to disseminate the use of RHS in households by giving financial support for the implementation of the systems. The viability of RHS has been assessed in the perspective of households extensively, resulting in the knowledge that some features of the systems are more relevant for the performance of the systems, such as the demand, the tariff, the capacity of the accumulation reservoir and the precipitation regime. So, the RHS Public Policies (RHSPP) will be tested for different configuration of systems and households as described below:

• Baseline scenario: this scenario considered that there were no RHS in the residence area.

• RL scenario: comprised of RHS with accumulation reservoir of 15 m³ attending two levels of non-potable water demand – only External uses (Ext - gardening and floor cleaning) or External and Toilet Flush demand (Ext & Tf).

• RS scenario: comprised of RHS with accumulation reservoir of 1 m³ attending two levels of non-potable water demand – only External uses (Ext - gardening and floor cleaning) or External and Toilet Flush demand (Ext & Tf).

The values of 1 m³ and 15 m³ for the reservoir capacity represent the lower and upper limits of the volume accumulation possibilities of the RHS, respectively. These values consider limitations such as available space in the land parcel and cost of investment of the system, given the high price of the reservoir. We decided to evaluate the performance of the system under these possibilities.

The following residential areas were included in this research: 1 = Vila São José; 2 = Veredas; 3 = Tradicional; 4 = Norte; 5 = Sul. The water consumption intervals and respective codes are: 1 = 0 – 7 m³; 2 = 8 – 13 m³; 3 = 14 – 20 m³; 4 = 21 – 30 m³; 5 = 31 – 45 m³; 6 = greater than 45 m³. The direct water revenue in each residential area and consumption interval defined in FN002B_{(r, i)} used the tariff structure defined by CAESB in 2022 for January, 1^st 2023 to July, 31^st 2023, according to ADASA Resolution nº 12 from November 18^th 2022 (Distrito Federal, 2022a). The same tariff structure was applied to the average tariff in Table 3, considering the value of R$ 8.82 for the price of the fixed parcel of the tariff structure. The CAESB tariff structure is based on the Increasing Block Tariff (IBT) methodology in which the price for water consumption is computed using various tariff ranges or intervals, with a unit cost that increases as consumption increases. Additionally, there is a fixed value of price added to the total charge to cover the connection maintenance and it does not depend on the water consumption volume.

Table 3
Average water tariff in each water consumption range based on the IBT methodology enforced in Brazlândia.

Consumption interval (m3)	WcVIn(i)	TfIn(i) (R$/m3)	TTfIn(i) (R$)	AvgTfIn(i)) (R$/m3)
0 to 7	7	3.26	22.82	3.26
8 to 13	6	3.91	23.46	3.56
14 to 20	7	7.75	54.25	5.03
21 to 30	10	11.24	112.40	7.10
31 to 45	15	16.86	252.90	10.35
Above 45		21.91	21.91	10.84

• Source: CAESB data (Companhia de Saneamento Ambiental do Distrito Federal, 2023).

For the parameters of the adapted indicators, besides the baseline scenario, computed as Brazlandia without RHS, the data from Federal District was added for the comparative analysis with the scenarios evaluated to Brazlandia and the residential areas.

For the cost-benefit analysis (CBA) of the RHS public policy, two of the scenarios described in this section 2.2 were selected:

1. RL scenario supplying water to External and Toilet Flush demand (Ext & Tf).

2. RS scenario supplying water to External uses (Ext - gardening and floor cleaning).

For the computation of expenses avoided (ExpR_{(c, s, f)}), the indicator IN026 for the Federal District was considered as R$ 4.18/m³ for the year of 2019 and the fraction of the costs related to water supply services as 58.5% for water supply services and 41.5% for sewage services. The cost of the services was based on the Financial Reports of CAESB for the year 2019 (Companhia de Saneamento Ambiental do Distrito Federal, 2019).

Table 4 presents the average tariffs (computed using Equations 10 and 11) considered in the economic balance analysis for water supply expansion in non-residential areas (commercial, industrial and public institutions).

Table 4
Average tariff in each consumption interval for users in commercial, industrial and public institution categories.

Consumption interval (m3)	Average tariff
	Commercial, industrial and public institutions
	(R$/m3)
0 to 4	6.72
5 to 7	7.44
8 to 10	8.46
11 to 40	12.20
Above 40	12.60

• Source: Contribution of authors based on data from Companhia de Saneamento Ambiental do Distrito Federal (2023) and Equations 10 and 11.

The water saving potential of RHS

This paper computed the water saving potential of RHS considering average values of rooftop surface areas in the study area and using methods in Pacheco & Alves (2023) e Sant’Ana et al. (2017).

The following Equations 1, 2, 3 and 4 present the mathematical basis for the evaluation of RHS potential according to Yield After Spillage - YAS model and using 0.8 as runoff coefficient and 2 mm for initial rainfall discharge when there were at least three consecutive days without no rain. Details can be found at Pacheco & Alves (2025).

$Va{r}_{\left(r,t\right)}=\left(Rd-ff\right).A.Cr/1000$ (1)

$Vr{c}_{\left(r,t\right)}=mín\left\{\begin{array}{c}P.V_{\left(t\right)}\\ \theta .Va{r}_{\left(t\right)}+Vr{r}_{\left(t-1\right)}\end{array}\right.$ (2)

$Vr{r}_{\left(r,t\right)}=mín\left\{\begin{array}{c}Va{r}_{\left(t\right)}+Vr{r}_{\left(t-1\right)}-Vr{c}_{\left(t\right)}\\ Ra-\left(1-\theta \right).Vr{c}_{\left(t\right)}\end{array}\right.$ (3)

$Cr{w}_{\left(r,i,T\right)}={\displaystyle \sum }_{\begin{array}{c}i=1\\ t=1\end{array}}^{r,T}\left(Vr{c}_{\left(i,t\right)}.N_{\left(i\right)}\right)$ (4)

where: Var= available rainwater volume in day t (m³); Rd= rainfall in day t (mm); ff= first flush rainwater (mm); A= average roof top surface area (m²); Cr= surface runoff coefficient; Vrc=rainwater volume consumption in day t (m³); V=average water consumption in day t (m³); P=percentage of non-potable consumption in total water consumption (%), 13 or 28; Vrr= rainwater volume in the reservoir in day t (m³); Ra= reservoir accumulation capacity (m³); ϴ= YAS coefficient (0≤ϴ≤1) – 0; N= number of water connections; Crw= Rainwater consumption in each residential area (m³); i= water consumption interval; r= residential area; t= day; T= month or year.

Performance analysis of the RHS Public Policy (RHSPP) including the Water Utility perspectives.

The economic analysis of RHSPP proposed in the present work uses indicators defined in the National Sanitation Information System (SNIS) and considered the following assumptions:

1. The RHSPP should receive financial support from the government in order to enhance urban water security, so the household economic evaluation of using RHS is not included in this analysis;

2. The analysis evaluated the potential of water saving using RHS compared to traditional sources of water supply operated by the Water Utility;

3. The economic assessment of the RHSPP is comprised of two main stages, the cost-benefit analysis and the economic balance analysis, both including the perspective of the Water Utility. The economic balance analysis includes the assessment of new business opportunities (NBO) that arises from the use of the volume of water saved due to the implementation of the RHSPP.

The SNIS data used in the research came from the year of 2019. The traditional values of water consumption volumes or charged in SNIS´s indicators substitute the water volume metered. In the study area, the simulation model considered the average household volumes for September 2019 which is the month of highest water consumption according to historical data from CAESB (Brasil, 2020b). The monthly data included number of connections, metered water consumption in each residential areas for each interval of water consumption defined in the tariff structure.

The metered water volume considered in the scenarios of RHSPP implementation were computed using Equations 5 and 6 and indicator AG008_(r) of the SNIS. The total rainwater volume captured and consumed in each scenario (Crwp_(s)) is the sum of the rainwater volume captured and used in all households of the residential area r in each scenario s (Crwp_{(s, r)}).

$$AG{008}_{(s,r)}=AG008B_{(r)}-Crw{p}_{(s,r)}$$ (5)

$$Crw{p}_{(s)}={\sum }_{(r)}Crw{p}_{(s,r)}$$ (6)

where: AG008_{(s, r)} = metered water volume in scenario s for each residential area r using RHSPP (10³ m³/year).

AG008B_(r) = metered water volume in the baseline scenario (without RHSPP) in each residential area r (10³ m³/year); Crwp _(s) = total potential rainwater harvested volume per scenario s (10³ m³/year); Crwp_{(s, r)} = total potential rainwater harvested volume per scenario s in each residential area r (10³ m³/year); s = scenarios: 1= RL – Ext demand; 2 = RL – Ext & Tf demand; 3 = RS – Ext demand; 4 = RS – Ext & Tf demand; r = residential areas: 1 = Vila São José; 2 = Veredas; 3 = Tradicional; 4 = Norte; 5 = Sul.

The benefit-cost balances including the perspective of the Water Utility was evaluated for different levels of water consumption in all residential areas for scenarios of RHSPP described in section 2.1. This analysis considered the loss of revenue a cost for the water utility when the RHSPP is applied. On the other hand, the reduction of operational and maintenance costs due to reduction of water volume negotiated by the Water Utility when the RHSPP is in place is considered a benefit in the benefit-cost analysis.

We based the water revenue on the indicator FN002B defined by the SNIS. The direct operational water revenue for the baseline scenario, FN002B, is computed as the sum of direct operation water revenues for the baseline scenario in all residential areas (FN002B_(r)) as illustrated in Equation 7. The FN002B_(r) is the sum of direct operation water revenue resulted from all water consumption interval i FN002B_{(r, i)}, according to Equation 8. The FN002B_{(r, i)} is computed using Equation 9, 10 and 11.

$$FN002B=\sum FN002{\left(B\right)}_{(r)}$$ (7)

$$FN002B_{(r)}=\sum FN002{\left(B\right)}_{(r,i)}$$ (8)

$$FN002B_{(r,i)}=[(NbCI{n}_{(i)}xCTf)+(AvgTfI{n}_{(i)}xAvgWcI{n}_{(i)}xNbCI{n}_{(i)})]x12$$ (9)

$$AvgTfI{n}_{(i)}=TTfI{n}_{(i)}/WcVI{n}_{(i)}$$ (10)

$$TTfI{n}_{(i)}=WcVI{n}_{(i)}xTfI{n}_{(i)}$$ (11)

where: FN002B = total direct operational water revenue for the baseline scenario per year (R$/year); FN002B_(r) = direct operational water revenue for the baseline scenario in r (R$/year); FN002B_{(r, i)} = direct operational water revenue for the baseline scenario in r for each interval i (R$/year); CTf = fixed connection tariff (R$); AvgTfIn_(i) = average tariff in each interval i (R$/m³); AvgWcIn_(i) = average water consumption in each interval i (m³); NbCIn_(i) = number of connections in each interval i (connection); TfIn_(i) = water tariff in each interval i (R$/m³) defined by the current tariff structure; WcVIn_(i) = water consumption volume in each interval i (m³) in current tariff structure; TTfIn_(i) = water tariff for the interval i (R$); i = water consumption interval index.

The direct operational water revenue in scenarios of RHSPP, FN002_(s), is computed according to Equation 12. The FN002 _{(s, r)} results from the subtraction of the revenue loss due to RHS in each scenario and residential area r (RevL_{(s, r)}) from the direct operation water revenue of the baseline scenario in each residential area FN002B_(r), expressed in Equation 13. RevL_{(s, r)} results from the sum of this variable for each water consumption interval (RevL_{(s, r, i)}), shown in Equation 14. The product of the potential of water saving and the average water tariff results in the expression of the revenue loss in each water consumption interval as illustrated in Equation 15.

$$FN{002}_{(s)}={\sum }_{(r)}FN{002}_{(s,r)}$$ (12)

$$FN{002}_{(s,r)}=FN002B_{(r)}–Rev{L}_{(s,r)}$$ (13)

$$Rev{L}_{(s,r)}={\sum }_{(i)}Rev{L}_{(s,r,i)}$$ (14)

$$Rev{L}_{(s,r,i)}=Crw{p}_{(s,r,i)}xAvgTfI{n}_{(i)}$$ (15)

where: FN002_(s) = direct operation water revenue in each s (R$/year); FN002_{(s, r)} = direct operation water revenue in each s and r (R$/year); FN002B_(r) = direct operational water revenue in the baseline scenario in each s and r (R$/year); RevL_{(s, r)} = revenue loss due to RHSPP in each s and r (R$/year); RevL_{(s, r, i)} = revenue loss due to RHSPP in each interval i, s and r (R$/year); Crwp _{(s, r, i)} = water saving potential due to RHS public policy in each interval i, s and r (m³/year).

The benefits of RHSPP in the perspective of the water utility is related to the reduction of expenses due to the decrease of water consumption from traditional source, (ExpR_{(c, s, f)}). This analysis used the IN026 and the DEX_W indicators from the SNIS data base. The following equations summarize the analysis.

$$Exp{R}_{(s,r,i)}=DE{X}_{W}xIN026xCrw{p}_{(s,r,i)}$$ (16)

$$BC{A}_{(s,r,i)}=Exp{R}_{(s,r,i)}-Rev{L}_{(s,r,i)}$$ (17)

where: ExpR_{(s, r, i)} = reduction of the water supply expenses due to RHSPP (R$); IN026 = total expenses related to water and sewage systems from traditional sources per volume (R$/m³); DEX_W = fraction of IN026 related to expenses of the water supply system; BCA_{(s, r, i)} = benefit-cost analysis (R$).

The expanded economic analysis included the value of alternative business or new opportunity of business that the water utility could invest using the volume of water saved by RHSPP. This extra volume could benefit new developments (urban area expansion) or water user categories with higher water consumption patterns. These alternatives are named as new business opportunities (NBO) in the present study.

The expenses associated with the expansion of the water supply system using the water volume of the RHSPP are computed using Equation 18 as follows.

$$NBOEx{p}_{(s,r,i)}=IN026xCrw{p}_{(s,r,i)}$$ (18)

where: NBOExp_{(s, r, i)} = expenses due to water supply system expansion (R$).

The revenue from water supply expansion or other NBO (NBORev_{(c, s, f)}) considers the sum of saved water volume in all water consumption intervals being sold to each water consumption interval. The sum results from the product of average tariff per water consumption interval and the volume multiplied by two, in order to take into consideration also the revenue of sewage collection in the new developments (or household users). The computation considers that the total water volume saved using RHSPP will be sold to other water consumption intervals.

$$NBORe{v}_{(s,r,i)}=\sum Crw{p}_{(s,r,i)}{x}_{}AvgTfI{n}_{(i)}x2$$ (19)

where: NBORev _{(s, r, i)} = revenue from water supply expansion or other NBO (R$).

The sustainable economic balance (SBE_{(s, r, i)}) of RHSPP includes all the revenue and expenses related to NBO of using the water volume saved to expand the water utility businesses and the revenues and expenses related to the reduction of water volume being used from the traditional water supply system which is represented by the BCA. The overall evaluation is shown in Equation 20.

$$SE{B}_{(s,r,i)}=\left[\sum NBORe{v}_{(s,r,i)}-\sum NBOEx{p}_{(s,r,i)}\right]+BC{A}_{(s,r,i)}$$ (20)

where: SEB_{(s, r, i)} = sustainable economic balance of RHSPP in each interval i, s and r (R$).

The economic analysis of RHSPP including the perspective of water utilities considers the balance between benefits from reduction of expenses and losses from revenue reductions. Advancing the analysis, the economic analysis also includes the benefits of selling the extra volume of water (saved from RHS) to other households with higher levels of consumptions or other categories of users, such as commercial, industrial and public institutions.

RESULTS AND DISCUSSION

In this item, the potential for water savings with the implementation of the systems and the cost-benefit of the systems were evaluated.

Water saving potential resulted from RHS public policy in Brazlandia/FD

The economic analysis of the RHSPP impact on water utility initiates by the computation of the potential water saving resulted from the RHSPP application. Figure 2 presents these results considering a 30-year precipitation time series and non-potable water demand in External areas and External areas and Toilet flushes.

Figure 2
Rainwater harvesting potential for different reservoir capacities and non-potable uses in external areas and toilet in Brazlandia.

There is a difference in water saving potential between residential areas; the South and Traditional sectors show lower volumes saved, while Vila São José and the North sector stand out for the larger volumes of rainwater used. This is due to the fact that total water consumption in these two sectors is high and the first two present the minimum values. For this reason, scenarios with external and non-potable demand resulted in greater potentials.

It is also noted that larger reservoirs result in greater water savings since the rainfall is the same for all scenarios. In any case, it can be seen that by doubling and tripling the storage capacity (from 5 to 10 and 15 m³) the potential for savings does not change significantly, given that the catchment area of residences remains fixed at small values.

Benefit cost analysis of RHSPP

The benefit cost analysis of RHSPP evaluates the impact of RHSPP for the water utility based on the computation of revenue loss and expenses avoided after the RHSPP implementation. Figure 3 presents the potential operational revenue losses in all residential areas of Brazlandia for the scenarios evaluated.

Figure 3
Potential operational revenue losses for all residential areas in Brazlandia for evaluated scenarios.

The potential reduction of treated water consumption after the implementation of RHSPP is around 125,962.60 m³/year, considering the scenario RS for external demands (gardening and floor washing) which is the simplest scenario to implement. This would represent a total operational revenue annual loss of R$ 582,889.92 for the water utility, corresponding to 0.06% of the annual operational revenue. The greatest revenue loss would be in scenario RL and demand Ext and Tf, R$ 1,711,478.83, approximately 0.18% of the operational revenue of the water utility.

The saved volumes of water will impact the volume of sewage charged by the water utility, given that the sewage tariff is based on the metered volume of water consumption. Given that the sewage volume generated by the RHS is evaluated based on the volume of water consumption and is not metered, the corresponding fraction of revenue is also lost. However the water volume captured by the RHS still generates sewage and it is collected and treated by the water utility.

This relationship awakens the importance of analyses of sewage expenses for the water utility after the RHS public policy. In this situation, the water utility will be treating a volume of sewage greater than the volume of water consumption from the traditional source. It is important to establish a mechanism to correct this loss of revenue due to the volume of sewage that is not charged in the current tariff structure.

Ward et al. (2019) showed that in Brazil and in the United Kingdom there are some efforts to define a modified tariff structure to consider the sewage generated from the RHS, in order to protect the water utility revenue. Article 39 of the ADASA Resolution nº 5/2022 defined the rules for the metering and charging of sewage services (Distrito Federal, 2022b). In the cases of rainwater harvesting and wastewater reuse, the rules in the Federal District will be defined in specific resolutions in the future.

Considering two extreme scenarios, the RS scenario for Ext demand and the RL scenario for Ext & Tf demand for all residential areas in Brazlandia, the cost benefit analysis for the water utility perspective resulted negative in the three initial water consumption intervals. In these cases, there is a loss of revenue greater than the reduction of expenses. This is illustrated in the results of Table 5. However, when considering the total cost-benefit balance for all consumption intervals for each residential area only for Traditional residential area resulted negative for both scenarios of demand. Based on the results of Table 5, one could expect that the RHSPP dissemination is actually favorable for the water utility in BAR.

Table 5
Cost benefit analysis of RHS public policies in the water utility perspective considering two extreme scenarios: RS – Ext demand and RL – Ext and Tf demand. (thousands of Real per year).

	Residential areas	Benefit-cost balance in each Water Consumption Interval					Total balance per residential area
		0 to 7 m3	8 to 13 m3	14 to 20 m3	21 to 30 m3	31 to 45 m3
Scenario RL – Ext & Tf Demand	Vila São José	-R$ 723.41	-R$ 622.76	-R$ 129.56	R$ 564.95	R$ 1,655.36	R$ 744.58
	Veredas	-R$ 218.81	-R$ 184.86	-R$ 18.48	R$ 215.80	R$ 583.63	R$ 377.28
	Norte	-R$ 431.39	-R$ 374.88	-R$ 98.00	R$ 291.89	R$ 904.03	R$ 291.65
	Tradicional	-R$ 139.21	-R$ 123.35	-R$ 45.65	R$ 63.76	R$ 235.54	-R$ 8.91
	Sul	-R$ 133.96	-R$ 118.02	-R$ 39.92	R$ 70.07	R$ 242.75	R$ 20.92
Scenario RS – Demand Ext	Vila São José	-R$ 248.11	-R$ 214.07	-R$ 47.24	R$ 187.68	R$ 556.53	R$ 234.79
	Veredas	-R$ 74.37	-R$ 62.91	-R$ 6.78	R$ 72.27	R$ 196.38	R$ 124.59
	Norte	-R$ 147.19	-R$ 128.00	-R$ 34.02	R$ 98.33	R$ 306.12	R$ 95.24
	Tradicional	-R$ 48.10	-R$ 42.65	-R$ 15.93	R$ 21.69	R$ 80.76	- R$ 4.23
	Sul	-R$ 45.80	-R$ 40.36	-R$ 13.70	R$ 23.84	R$ 82.78	R$ 6.76

There is a lack of studies that carry out the economic evaluation of RHS from the perspective of sanitation companies. A study that carried out this evaluation for different Brazilian cities (Pacheco & Alves, 2025) found that in all cities there is a reduction in profits for the sanitation company, but the cost-benefit analysis remains positive with the implementation of RHS on a large scale.

So far, the economic assessment carried out in this study takes into consideration only the reduction of water consumption volume when RHS substitutes the water consumption from traditional system. It does not include the possible gain of revenue if the saved water volume is used for other residential areas or be sold to other categories of water users that pay higher charges or prices per cubic meters of water.

The next stage of the economic analysis expands the analysis and searches for mechanisms that could protect the water utility financial sustainability and also identify other social benefits of the RHSPP, such as increase in the water security, expand the water access to other residential areas or serve other categories of water use with higher economic return to the water utility (commercial, industrial or public institutions). The present work analyzed these alternatives as New Business Opportunities (NBO) and included them in the overall economic balance of RHSPP in the water utility perspective.

The savings from RHS would occur mainly during rainy seasons, allowing the water utility to expand their water supply system to additional residential areas or to other categories of users. It would also be possible to accumulate water for the dry season to enhance the water supply system reliability and reduce risks of water crisis. Figure 4 illustrates the overall economic balance of the RHSPP if all the water volume saved could be negotiated or sold to each of the water consumption intervals. We can see that the overall economic balances for the three initial intervals are not positive, given the low levels of water charges (prices) in these intervals according to the current water tariff structure. But if all the water volume saved by RHS public policies be sold to households that use water in the higher consumption intervals (greater than 21 m³) there would be positive results for the water utility. Actually, considering all the water users in each residential areas, the total economic balance for the residential areas is all positive, except for the Tradicional residential area. It is also important to note that Vila São José can have great impact in this analysis given the great number of households in this residential area resulting in major source of water saving that could be directed to users that pay higher prices for the water or to expand the access to water in new residential areas.

Figure 4
Sustainable economic balance of NBO of selling the water saved by RHS to other residential areas in scenarios of Ext demand and Ext & Tf demand.

If the water volume saved due to RHS could be sold to different water user categories (commercial, industrial or public institutions) there would be profit for the water utility in all water consumption intervals in all residential areas as shown in Figure 5. In this case, the RHS public policy would have a positive economic assessment. This scenario requires that the amount of water available reaches the demand of categories of users with higher charges, even outside of the residential area.

Figure 5
Sustainable economic balance of NBO of selling the water saved by RHS to commercial, industrial and public institutions, according to Ext demand and Ext & Tf demands.

The results indicate that the implementation of RHS can be beneficial for the utility, as it contributes to reducing potable water consumption and alleviating pressure on supply infrastructure. This is an important link between sanitation sector and the urban water resources management that can be emphasized by means of public policies adjusted to local conditions (climate and socioeconomic characteristics). However, the success of these systems depends not only on their technical and economic feasibility but also on the establishment of public policies that promote their adoption. In this regard, the work of Sant’Ana et al. (2017) presents an important approach by proposing a differentiated tariff (Premium Tariff) as a public policy measure. This tariff could either be fixed, subject to adjustments based on increases in operating costs, or function as a temporary mechanism to encourage property owners to invest in rainwater harvesting and gray water reuse systems. Based on this study, the feasibility of this first Premium Tariff option can be simulated for the Federal District. Specifically, for the scenarios evaluated in Brazlândia, an increase of R$ 0.014/m³ per month per connection would provide financial support to the sanitation company.

In any case, for incentive policies to effectively promote the widespread adoption of RHS, further research is needed on how institutional and socio-political support can be directed to enhance their effectiveness and increase public acceptance (Campisano & Lupia, 2017). Additionally, this assessment should consider not only the cost of capital, the demand for rainwater, and the price of distributed water but also the environmental benefits associated with water conservation and urban drainage improvements.

CONCLUSIONS

This work proposed and applied a methodology to evaluate the impact of RHS public policies in the perspective of the water utility. The procedure includes the impact of the implementation of RHSPP across different patterns of household’s water consumption in urban areas. The methodology proposes a benefit cost analysis of the RHSPP for the water utility that incorporates also the economic balance of new business opportunities that arises upon the RHSPP implementation.

The procedure was applied to Brazlandia in the Federal District of Brazil. The analysis demonstrated that RHS have the potential to supply 57.14% to 99.85% of the total External demands (floor cleaning and gardening), considering all the residential areas. If toilet flushes are added to external demands for the RHS, the systems are able to supply from 42.27% to 90.45% of the demand.

The cost benefit analysis of RHS public policies applied to households in the three lower water consumption intervals in Brazlandia, demonstrated a negative balance once the reduction of revenue from water and sewage services are greater than the reduction of expenses. However, the same analysis results in positive balance for the households in the upper water consumption intervals leading to an overall positive economic balance when considering all the ranges of household water consumptions.

In this way, the analysis of the benefits of implementing RHS for the water utility indicated a reduction in revenue from water and sewage services, despite a decrease in the costs of providing water services. Therefore, public policies should be considered to subsidize the water utility. However, if all the water saved through the implementation of RHS is sold by the company to other residential areas or to consumption brackets above 20 m³, it could create an opportunity for economic gain. The same applies if the water is sold for non-residential uses. The methodology proved enlightening and easy to replicate in other urban areas in Brazil.

ACKNOWLEDGEMENTS

The authors thank University of Brasília Graduate School for its support.

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Edited by

• Editor-in-Chief:
  Adilson Pinheiro

• Associated Editor:
  Iran Eduardo Lima Neto

Publication Dates

• Publication in this collection
  13 June 2025
• Date of issue
  2025

History

• Received
  21 Jan 2025
• Reviewed
  08 Mar 2025
• Accepted
  03 Apr 2025