The next big source of drinking water may be your toilet.
As a record-breaking drought drags on in California and elsewhere, regulators and residents are overcoming squeamishness about recycling wastewater—yes, sewage—to boost scarce water supplies. These so-called toilet-to-tap projects have been taking hold in the American West, Australia, and Europe, and the state of California is now considering vastly expanding such efforts.
When wastewater is recycled, it first goes to a sewage treatment plant—just like all wastewater. Then it gets sent to another facility connected to the treatment plant that’s been equipped with technologies to purify the water to a much higher quality. Water has been recycled for agricultural and industrial purposes for decades, and in those cases it isn’t treated to drinking water standards—it’s just treated to eliminate pathogens and other public health concerns.
But the newer facilities are aiming higher: They are looking to more thorough and more advanced treatment processes, such as reverse osmosis and potentially zero-liquid discharge, to get the water to near-distilled quality. These projects are costly. The most advanced technologies are very expensive, and there are a lot of materials involved—miles and miles of pipes, for example—and especially in urban settings, there’s also the cost and disruption of tearing up roads to lay down those pipes. But, said Randy Barnard, chief of the recycled water unit for California’s State Water Resources Control Board, as the costs of new sources of water continue to climb, the costs of laying the infrastructure for water recycling look more affordable.
California has about eight recycled water projects—in Los Angeles, Santa Barbara, and Orange counties—that use what’s called groundwater replenishment: Treated wastewater is added to reserves of groundwater, which is pumped to a treatment plant that supplies a city with its water. In Orange County, which is thought to operate the largest potable water reuse system in the world, water is sent from the wastewater treatment plant to a facility that uses three treatment steps: microfiltration, reverse osmosis, and then ultraviolet light mixed with hydrogen peroxide, which destroys any trace compounds that survived the first two steps. The water is then sent out to basins in Anaheim, where it filters through sand and gravel and into the underground aquifers. The facility has been up and running since January 2008 and can produce 70 million gallons of water a day—enough for about 600,000 residents.
The state has set a target to recycle 815 billion gallons of water a year by 2030. (The current rate is about 408 billion gallons annually, up from 163 billion gallons in 2002.) Barnard said that although the target represents a fraction of the state’s water consumption, it diverts a huge amount of wastewater from being dumped in the ocean.
California is now exploring regulations that would allow cities to eliminate the middle step of groundwater filtration. Under “direct potable reuse,” wastewater is treated more to meet drinking quality standards and then piped directly into the city’s water supply.
It’s not just California: Cities around the world and across the country, mainly in Southwestern states, have water reuse projects in place, and others, including Brownwood, Texas, and Cloudcroft, New Mexico, may get under way soon. The state of Texas has approved a direct potable reuse project for Brownwood. If built, it could supply 30 percent of the city’s water.
Public relations, not technology, has been one of the biggest challenges.
When San Diego proposed a recycled water project a decade ago, media coverage scared people off. “Then San Diego did all kinds of outreach, workshops,” said Barnard. “That turned the public perception around. Now, 10 years later, it’s been a total 180. If the local population doesn’t want recycled water, they’re not going to vote for it, and it won’t move forward.”
San Diego, which relies on the Colorado River and Northern California for 85 percent of its water, hopes recycled water will supply a third of its needs by 2035.
In the meantime, the city continues to explore the potential for both indirect and direct potable reuse projects. Sarah Mojarro, a spokesperson for San Diego’s Public Utilities Department, said the city is partnering with the WateReuse Research Foundation to investigate two other treatment processes—ozonation and biological activated carbon filters—as additional safeguards to protect and ensure water quality.
In Orange County, officials say residents were surprisingly receptive to the idea of the groundwater replenishment project from the start. In an opinion poll released earlier in the year, the San Diego County Water Authority found that 73 percent of people favored the idea of supplementing the drinking water supply with recycled water.
The state has long had to be mindful of how it sources its water, but as supplies grow increasingly scarce, more people are realizing it makes more sense to capture and recycle their wastewater than send millions of gallons of it to the ocean every day.
“It’s much easier to move to potable reuse in places like California and New Mexico than it is to start piping water from the Great Lakes,” said Adam Krantz, chief executive of the National Association of Clean Water Agencies. “Think about how many miles of pipe, how much energy, that would take. The argument for potable, industrial, and agricultural reuse is only more obvious given the ongoing drought.”