California's First Recycled Water Recreational Lake

Santa Margarita Water District worked with the City of Mission Viejo and the Lake Mission Viejo Homeowners Association to make a historic change in water use in Orange County. With the construction of an Advanced Purified Water treatment facility, Lake Mission Viejo became the first recreational lake in California to use Advanced Treated water for refill. This new system will save more than 100 millions gallons annually of drinking water for other uses.

The treatment method involves taking already highly treated wastewater and treating it further in a process that includes advanced filtration tanks, reverse osmosis and ultraviolet light. This additional purification makes it safe to supply the lake for swimming and other recreational activities.

Ironically, the state was gripped by drought when the lake was built in 1976. It was finally filled in 1978. The lake loses about 500,000 gallons a day to evaporation--enough water to supply about 1,400 families for a year.

In 2015, as the current drought continued to tighten its grip on the state, SMWD officials grew concerned about continuing to pump drinking water into the recreational facility.

The water district approached the Lake Mission Viejo Association last year about using Advanced Treated Water to replenish the lake. Homeowners overwhelmingly approved the change. The City of Mission Viejo subsequently agreed to loan SMWD $3 million for the project and also provide a $1 million grant to help the water district build the new treatment facility to purify the recycled water. The water district will pay off the loan over 20 years, at 2.5 percent interest. The agreement also calls for the city to receive enough recycled water to irrigate about 80 percent of its parks, medians and slopes for 25 years at a discount. The Lake Association will repay Santa Margarita an estimated $5.1 million in construction costs over 20 years.

The Lake Mission Viejo Association (Association) owns and operates the 124-acre lake located at Alicia Parkway and Marguerite Parkway in Mission Viejo.  The lake, which holds approximately 350 acre feet of water, is maintained with a combination of water sources, including potable water supplies provided by Santa Margarita Water District.

In light of the ongoing drought conditions and in support of future water supplies, the Association evaluated alternative water sources to replace the use of potable water from the District.  The idea is to maintain lake water elevation levels with a sustainable, reliable, cost-effective source of local non-potable water that meets the water quality standards desired for the continued recreational use of the lake.

At the same time, the District is working to maximize its supply of potable water for domestic use. SMWD currently produces recycled water that is treated to standards for irrigation and other non-potable uses in accordance with Title 22 of the California Code of Regulations, including for use in recreational lakes.

The Association currently purchases this recycled water from SMWD for irrigation.  While Title 22 water can legally be used in the lake, the Association has determined that the Association members want a higher water quality standard for the recreational uses of the lake by the members. The District, working with the Association, has determined that with additional treatment infrastructure, it can produce higher quality recycled water to meet the needs and demands of the Association at the lake.

What is Advanced Treated Water (ATW)?

Advanced Treated Water is recycled water that has received additional levels of treatment to polish the water to the Lake Mission Viejo Association’s water quality specifications.

Is Advanced Treated Water safe?

Yes, Advanced Treated Water is safe for recreational activities, including swimming, at Lake Mission Viejo. Prior to the extra treatment, Santa Margarita Water District’s recycled water meets state and federal health regulations for swimming lakes (Title 22 of the California Code of Regulations).

Is Advanced Treated Water safe for human consumption?

While no ill effects would be anticipated from consuming Advanced Treated Water, it is not yet approved for human consumption.

SMWD currently produces recycled water that is treated to standards for irrigation and other unrestricted non-potable uses in accordance with Title 22 of the California Code of Regulations (“Title 22”); including for use in recreational lakes. 

LMVA currently purchases Title 22 recycled water from SMWD for irrigation and while Title 22 water can legally be used in the Lake, LMVA has determined that a higher water quality is desirable to maintain the lake quality to support the various recreational uses of the Lake by LVMA members. The District, in consultation with LMVA, has determined that with additional treatment infrastructure, it can produce higher quality recycled water to such standards and in adequate quantities as are necessary to meet the needs of LMVA at the Lake.

How much will the project cost?

The projected is expected to cost $5 million. The project is estimated to pay a premium for the water for 20-25 years

Who will pay for the project?

The Lake Mission Viejo Association will pay the capital costs of the ATW treatment facility and for the water that is ultimately delivered for use in the lake.

Who approved the project?

Delegates representing the 81 neighborhoods within the 24,217-home Lake Mission Viejo Association voted unanimously to switch to Advanced Treated Water for lake refill and end nearly 40 years of using potable (drinking) water to maintain water levels in the 124-acre Orange County lake. In all, delegates cast 19,803 votes – representing 82 percent of the Association’s homeowners – all in favor of the Association working with the Santa Margarita Water District to construct a new treatment plant to produce Advanced Treated Water for the lake.