Water Resources

Water Resources Western invests in reliability projects to secure water supply both for our customers
and the region. These investments focus on securing new water rights via stormwater capture, water wheeling from outside our service area, water recycling and groundwater desalting. We believe that reliable water resources are imperative for those not-so-rainy
days and years that are common to Southern California.

Desalting of water is usually associated with oceans, but not in the Inland Empire. Western began investing in desalting technology two decades ago to diversify its water supplies with construction of the Arlington Desalter, which was the first groundwater desalter created in Southern California. Opened in 1990 and expanded in 2004, the Arlington Desalter allows for the clean-up of local groundwater to provide high-quality drinking water for the region. In partnership with several other inland agencies, Western is also working to clean-up groundwater and expand local water supplies with additional desalters in the Chino Basin. These techniques and facilities also allow for additional groundwater storage opportunities. 

Seeking water rights is another way Western is securing water for our customers. The District fought for almost two decades to access rights to runoff water stored behind the Seven Oaks Dam. Western and San Bernardino Valley Municipal Water District partnered to secure these new water rights. In a wet year, captured runoff can yield up to 200,000 acre-feet of water, more than 1.78 million gallons per day. 

Reliable water supplies are critical to our customers’ way of life and our region’s economic vitality.  


Extended Emergency Regulation for Statewide Conservation

On May 18, 2016, the State Water Resources Control Board (State Board) modified the February 2016 extension of the emergency regulation to include calculation of an alternative water conservation standard based on a “stress test” approach that assumes three additional dry years. The alternative conservation standard is calculated by comparing the average annual customer demand from 2013 and 2014 to the available supplies in 2017, 2018, and 2019 assuming the three-year hydrology of 2013, 2014, and 2015. As part of this extended emergency regulation, agencies providing wholesale water supplies (such as Western Municipal Water District) are required to publicly post the volume of water that they expect to deliver to retail water suppliers in the next three years.

Wholesale Water Supply Certification

Western Municipal Water District has evaluated its water supply conditions using the methodology developed by the State Board. Western has calculated that it has sufficient supplies to meet the demands of retail water suppliers within the District’s general service area for the three-year certification defined by the State Board. It is important to note that not all of the water suppliers within Western’s general service area currently receive or requested supply for the three-year certification period.

Western would like to recognize the tremendous efforts residents and businesses throughout western Riverside County have made in the last decade to decrease water waste and increase the efficient use of water throughout the District’s general service area. The reduced water demands of 2013 and 2014, which are used in the State Board’s calculation, are a direct result of long-term customer conservation actions.

Based on coordination with the retail water suppliers regarding the amount of local water resources available in the three-year certification period, Western has estimated the wholesale demands for each agency. Western currently has two sources of supply from which it delivers in a wholesale capacity. Western purchases imported water from The Metropolitan Water District of Southern California and operates a brackish groundwater desalter in the Arlington Basin – the Arlington Desalter. Wholesale delivery details for the purposes of State Board certification can be found in the table and document links below.

Questions about this process or Western’s wholesale certification can be addressed to Western’s Director of Water Resources, Tim Barr at tbarr@wmwd.com.


Western Wholesale Supplies Available - revised 07/26/16

Backup Documentation:
Imported water supply information from Metropolitan Water District
Western's 2015 Urban Water Management Plan
Arlington Basin Groundwater Management Plan
Chino Basin Desalter Authority Water Supply Information


Retail Water Supply Certification

Western Municipal Water District has evaluated its retail water supply conditions using the methodology developed by the State Board. Western has calculated that it has sufficient supplies to meet the demands of retail water customers for the three-year certification defined by the State Board.

Western's Retail Certification 2016

Questions about Western's retail certification can be addressed to Western's Water Resources Analyst, Karly Gaynor, at kgaynor@wmwd.com