How much potable water is saved by wastewater recycling? Quasi-experimental evidence from California

Resources, Conservation & Recycling (Elsevier) | October 6th, 2021

Recently, California has made large investments in wastewater recycling to replace applications that use potable water. It may be expected that the use of recycled water

Recently, California has made large investments in wastewater recycling to replace applications that use potable water. It may be expected that the use of recycled water reduces potable water use, but such an equivalency is not assured. The addition of recycled water infrastructure in a large Californian water district creates a natural experiment where this work tests how recycled water usage affects primary potable water. This is done using econometric methods for causal inference in an observational setting that mirror a randomized control trial (RCT). From 2001 to 2014, a number of public parks were given recycled water infrastructure, while others in those regions remained exclusively on potable supply. A two-way fixed effects regression is used to produce a difference-in-differences estimate of the average treatment effect of recycled water on total and potable water usage. The results indicate that potable water usage is reduced significantly when a park is connected to the recycled water supply. The estimated rate of displacement in the study period is 81.7%, meaning each unit of recycled water use avoided 0.817 units of potable water usage, which implies the connection of parks to recycled water supply increases total water use. The analysis provides, to the best of our knowledge, the first empirical estimate of the water savings claimed by urban water recycling programs, and the first empirical estimate of displacement using quasi-experimental methods. The methodology can be utilized to evaluate the effectiveness of recycling programs around the world.

Identifying the Amount of Wastewater that is Available and Feasible to Recycle in California

Water Research Foundation (WRF) | July 24th, 2023

Influence of Urban Areas on Surface Water Loss in the Contiguous United States

American Geophysical Union (AGU) | February 7th, 2022

Installation of Bioretention Rain Gardens to Achieve Pollutant Reduction

San Francisco Estuary Institute (SFEI) | December 1st, 2019

Green infrastructure (GI) is a resilient approach to managing stormwater at its source while also delivering environmental, social, and economic benefits. GI uses vegetat

Green infrastructure (GI) is a resilient approach to managing stormwater at its source while also delivering environmental, social, and economic benefits. GI uses vegetation, soils, and other elements to restore more natural watershed processes that mimic nature to soak up stormwater, provide habitat, clean the air, and filter out pollutants from urban stormwater runoff. GI can reduce peak flows and stream erosion; recharge groundwater; and improve water quality in urban stormwater that drains to San Francisco Bay. 

Integrated Water Resources Plan 2015 Update

Metropolitan Water District of Southern California (MWD) | January 1st, 2016

In California water, uncertainty comes with the territory. Being unprepared for tomorrow, however, is simply not an option. The Metropolitan Water District of Southern C

In California water, uncertainty comes with the territory. Being unprepared for tomorrow, however, is simply not an option. The Metropolitan Water District of Southern California prepares for tomorrow with an evolving long-term water strategy known as its Integrated Water Resources Plan, or IRP. The inaugural IRP was adopted in 1996, with updates in 2004 and 2010. The 2015 IRP Update continues the tradition of assessing and adapting to changing conditions facing Southern California. The fundamental goal of the IRP is for Southern California to have as reliable a water system for tomorrow as the region has enjoyed for decades, regardless of the challenges that emerge along the way. Metropolitan plans to meet this goal through an adaptive management strategy that is the cornerstone of the 2015 IRP Update. Metropolitan was authorized by the California Legislature in 1928 to advance a regional approach to water supply in Southern California. Metropolitan’s initial mission was to construct the 242-mile Colorado River Aqueduct to its service area on the Southern California coastal plain. Metropolitan’s service area had an assessed property valuation of approximately $2 billion at the time. Now Metropolitan serves a six-county service area with a property valuation of approximately $2 trillion. Metropolitan imports supplies from both the Colorado River and Northern California via the State Water Project while investing in a variety of storage, local supply and conservation initiatives. Metropolitan has a long record of promoting alternatives to imported water supplies, dating back to the 1980s. With the IRP, that process became more formalized as a long-term strategy and official policy. Metropolitan has steadily diversified the future water portfolio for Southern California with each revision to the IRP. This update is no exception. Investments to maintain the reliability of imported supplies are complemented by an expansion of local supply development along with a reduction in demand through a variety of conservation and water-use efficiency initiatives. The necessary suite of actions evolves over time based on the water conditions of tomorrow. Updating the IRP creates a new baseline for managing into the future.

Investigation on the Feasibility of Developing Uniformwater Recycling Criteria ror Direct Potable Reuse

California State Water Resources Control Board (SWRCB) | December 1st, 2016

The population of California is projected to increase from 38 million to 50 million by the year 2049. This population increase will have a dramatic impact on the water ne

The population of California is projected to increase from 38 million to 50 million by the year 2049. This population increase will have a dramatic impact on the water needs of the State. To address this increased water need, the State will take a variety of actions as outlined in the Governor’s California Water Action Plan, first released in 2014 and recently updated in 2016 (CA Natural Resources Agency, 2016). One component of that plan is to increase the use of recycled water. The State Water Board has set a mandate of increasing the use of recycled water by 200,000 acre-foot per year (AFY) by 2020 and an additional 300,000 AFY by 2030. Although the use of recycled water for non-potable uses such as agricultural and landscape irrigation is already well established and has been regulated for decades in California, increasing the use of recycled water for both non-potable uses as well as a source of potable water (“potable reuse”) is important for the State to be able to meet this mandate. For example, groundwater replenishment (groundwater recharge), which is an indirect form of potable reuse, has the capacity to reuse 200,000 acre-feet of recycled water a year via just eight projects throughout California. Accordingly, the State Water Board revised and adopted uniform water recycling criteria for groundwater replenishment in 2014 and is in the process of establishing uniform water recycling criteria for the augmentation of surface water reservoirs used as a source of drinking water supply, which is another form of indirect potable reuse.

LA Sustainable Water Project: Los Angeles City-Wide Overview

University of California, Los Angeles (UCLA) | February 1st, 2018

This report assesses the potential to improve water quality standards while integrating complementary One Water Management practices that can increase potential local wat

This report assesses the potential to improve water quality standards while integrating complementary One Water Management practices that can increase potential local water supplies for the City of Los Angeles (the City).  This final report summarizes the current practices and future opportunities at the City-owned Water Reclamation Plants and underlying groundwater basins and highlights the importance of considering all aspects of integrated water management even when dealing with water quality or supply-focused projects. Implementing watershed-scale best management practice programs to meet stormwater permit requirements will significantly improve water quality in all watersheds.  However, additional mechanisms such as increasing Low Impact Development implementation and comprehensive source tracking and source control mechanisms will be required to potentially eliminate water quality exceedances.  There are multiple efforts occurring in the City and the region to increase the recharge of recycled water into the ground and the volumes of remediated groundwater extracted. This research further assessed the impacts of potential water supply portfolios, with greater volumes of locally-supplied water, on GHG emissions and energy needs of supplying LA’s water.  Conservation will be another powerful tool to decrease our dependence on imported water.  This research demonstrates the complex interrelationships between all aspects of urban water management, including, for example, stormwater management and local water supply.

Large Landscape Urban Irrigation: A Data‐Driven Approach to Evaluate Conservation Behavior

American Geophysical Union (AGU) | April 30th, 2019

Do businesses, multifamily residences, and homeowners associations irrigate differently than single‐family residences? Do customers who have recycled water irrigate di

Do businesses, multifamily residences, and homeowners associations irrigate differently than single‐family residences? Do customers who have recycled water irrigate differently than if they have potable water? How does water use change during drought and under different policy regimes? Is neighborhood affluence related to conservation behavior by nonresidential irrigation customers? These questions are all important for water managers planning how much water they need when and where, in the present and in the future. In this paper, we statistically investigated and modeled water use in a case study service area to examine how water demand for nonresidential large landscapes changed during a historic drought. The findings of this paper can help water managers understand urban water use behavior, which is useful for supply planning, targeting conservation efforts, and optimizing infrastructure investment.

Large Landscape Urban Irrigation: A Data‐Driven Approach to Evaluate Conservation Behavior

American Geophysical Union (AGU) | January 30th, 2019

Do businesses, multifamily residences, and homeowners associations irrigate differently than single‐family residences? Do customers who have recycled water irrigate di

Do businesses, multifamily residences, and homeowners associations irrigate differently than single‐family residences? Do customers who have recycled water irrigate differently than if they have potable water? How does water use change during drought and under different policy regimes? Is neighborhood affluence related to conservation behavior by nonresidential irrigation customers? These questions are all important for water managers planning how much water they need when and where, in the present and in the future. In this paper, we statistically investigated and modeled water use in a case study service area to examine how water demand for nonresidential large landscapes changed during a historic drought. The findings of this paper can help water managers understand urban water use behavior, which is useful for supply planning, targeting conservation efforts, and optimizing infrastructure investment.

Lawns and Water Demand in California

Public Policy Institute of California (PPIC) | June 26th, 2006

Over the next 25 years, outdoor water use will be a major factor in escalating water demand in California. The demand will be aggravated by the dominant land-use pattern

Over the next 25 years, outdoor water use will be a major factor in escalating water demand in California. The demand will be aggravated by the dominant land-use pattern in inland areas: single-family homes with lush lawns. Without efforts aimed specifically at reducing outdoor urban water use, the demand will pose significant financial and environmental challenges for California. In this issue of CEP, the authors analyze population growth and housing trends in the state’s major climactic regions, estimate residential lot and yard sizes, and examine the water needs of cool-season turf grass lawns. They also evaluate several outdoor water conservation programs.