A City Wide Assessment of the Financial Benefits of Rainwater Harvesting in Mexico City

Abstract

We assess the potential financial benefits of rooftop rainwater harvesting (RWH) in Mexico City from the perspective of property owners and entrepreneurs. A bottom‐up approach was followed by evaluating RWH at individual buildings and aggregating the results to a borough/city level. We consider sector‐specific water demands, potable and nonpotable uses, and user‐specific water tariffs. We find that RWH is economically most beneficial for nondomestic users rather than for small domestic users, who are often the target of RWH interventions. Based on a net present value analysis, a potable RWH system is not favored for most domestic users under the current subsidized municipal water tariff structure. Our analysis only considers capital and maintenance expenses, and not other benefits related to increased access to water and reliability, or social benefits from a switch to a RWH system. If the initial capital expense for RWH is partly financed by transferring the water subsidy to an entrepreneur, then RWH becomes financially attractive for a wide range of domestic users. To improve water access in Mexico City, RWH is attractive in the most marginalized boroughs where water use is currently lower and precipitation is higher. For domestic users relying on trucked water, RWH can have great financial benefits. Our approach provides quantitative data with high spatial specificity, highlighting the places and types of users that would benefit most from RWH.

Optimizing Household Water Decisions for Managing Intermittent Water Supply in Mexico City

“…However, when piped water is subsidized, rainwater harvesting is only economically optimal when piped supply is so limited that households must rely on secondary, more expensive water sources. This is consistent with other rainwater harvesting research, which has shown that the economic benefits of rainwater harvesting are highly dependent on municipal water rates. ,, Since piped water is often heavily subsidized, either directly or through government-funded infrastructure projects, a comparison to the price of subsidized piped water minimizes the value of rainwater, especially in areas with robust water supply and infrastructure . Additionally, rainwater harvesting may provide many community-wide co-benefits (e.g., decreased pressure on strained water supplies, flood reduction ,− ) not considered in our model.…”

“…This study, and others like it, could be strengthened by larger scale household data collection, and particularly detailed data collection around household water consumption, that would allow for an investigation of where households would fall on the presented trade-off curves. Important input data, such as number of people per household, rainfall depth, and household roof area, often vary widely across the city, contributing to the variability of water scarcity across small distances and brief time periods; a system-wide analysis must consider this heterogeneity. Optimal interventions for households can be explored by comparing Pareto fronts for different scenarios and identifying ones that allow for the lowest costs at high reliability; a minimum volume of piped water and sufficient storage are important for reducing costs for households.…”

“…Households employ a wide variety of water storage infrastructure, including underground cisterns, rooftop storage tanks, large buckets, and assortments of small storage vessels, with capacities varying to deal with intermittency. ,,,, Although previous studies have shown storage to be ubiquitous in areas with IWS, its contribution to water access reliability is poorly understood. Water storage allows households to access multiple sources of water (e.g., water trucks, private or public wells or boreholes, bottled water, or rainwater). ,,, Water trucks deliver bulk volumes of water to residents’ homes, typically at a much higher cost than the municipal piped water, and are common in communities with IWS. ,− Rainwater harvesting has been posed as a potential solution to water scarcity in cities worldwide because of its benefits to households as a low cost water source, although the financial viability of sophisticated collection systems has been contested. − At the municipal level, rainwater harvesting has been promoted to delay costly expansions of centralized water systems and provide co-benefits of flood control and conservation. ,− …”

The Influence of Deep Uncertainties in the Design and Performance of Residential Rainwater Harvesting Systems

“…(Central Bank 2021). The runoff surface coe cient was set to 0.8 and an initial water discharge of 2 mm was applied (recommended in the NBR 15527) in the case of three consecutive dry days (with less than 1 mm of rainfall) (Larrauri et al 2020). The selection of the ideal volume for the lower reservoir was based on the e ciency criteria de ned as the rate between the increase in the supplied water from the RWHS per increase in the reservoir volume.…”

Influência das incertezas no regime pluviométrico no aproveitamento de água pluvial em três cidades de Goiás - Brasil

“…O programa inicialmente efetua uma simulação contínua do balanço hídrico considerando o método do consumo de água depois do enchimento do reservatório (Yeld After Spillage -YAS), que proporciona resultados mais conservadores (FEWKES e BUTLER, 2000;MITCHELL, 2007). Foi adotado um descarte inicial de 2 mm, recomendado pela NBR 15527 (ABNT, 2019), quando há ao menos três dias consecutivos sem precipitação (precipitação inferior a 1 mm), conforme Larrauri et al (2020).…”