Recycled water is not a new idea. Treated wastewater was used to irrigate Golden Gate Park from the early 1900s through the 1970s.
Until recently, recycled water has been dedicated to non-potable uses such as irrigation, industry or toilet flushing. The largest user in the East Bay is the Chevron oil refinery. The challenge for water agencies has been that these uses require a second set of pipes - often colored purple to clearly differentiate them from pipes carrying drinking water. While all downtown high-rise buildings in San Francisco constructed since the 1980s have included purple pipes, there has been no way to convey recycled supplies from the city's treatment plants, and the toilets are flushed with drinking water.
Advances in technology, primarily the advent of modular reverse osmosis filters, are changing the landscape for recycled water.
After filtration, recycled water supplies are now more pure than other supplies. Still, in Orange County at California's largest recycling plant, to encourage public acceptance the recycled water is used to replenish the groundwater system, then retrieved and treated again before being blended with other drinking-water supplies.
Public education is helping to change the perception of recycled water. Singapore has led the way with a deliberate campaign that has involved the nation's prime minister and celebrities drinking recycled water, or "NEWater," on television. San Diego has educated its public and found a marked increase in acceptance over the past few years - a critical factor as it considers blending its recycled supplies, after another round of treatment, into its potable supply. Such "direct potable reuse" will require permission of the state Department of Health Services.
At $1,500 to $2,000 per acre-foot, recycled water is expensive - but about the same price as the ill-fated water transfer proposal that San Francisco tried to negotiate with the Modesto Irrigation District in 2012. The state water board is an enthusiastic supporter of recycling - having set a goal of about 2 million acre-feet per year by 2030, or 25 percent of statewide urban use - citing its benefits to local reliability, reduced environmental impacts to natural waterways, and insurance from drought.