Cities of the Tri-Valley and their water agencies are searching for a way to avoid more punishing drought years. But one proposed method, while touted as a "drought-proof" water option, has to overcome the "ick factor" that affects public support.

The cities of San Ramon, Dublin, Pleasanton and Livermore, along with the Dublin San Ramon Services District (DSRSD), Zone 7 Water Agency and Cal Water's Livermore division, plan to research how to bring indirect potable reuse to the Tri-Valley. But the more common moniker -- detested by some water officials for the off-putting imagery -- is toilet-to-tap.

By reusing wastewater and treating it to drinking water standards, millions of gallons of water that is dumped into the San Francisco Bay each year could be kept in the Tri-Valley, according to Leonard Olive, Pleasanton's assistant director of operations services.

"There's only so much water. Water isn't just made," Olive said.

A public survey done in late 2015 to evaluate public opinion of toilet-to-tap across the Tri-Valley showed 63% of those polled support the idea of supplementing the region's water supply with treated reused water. Those that support the idea cite the drought as their main concern, but those that are against the idea say they are worried the process isn't safe -- or just can't get past the "ick factor," as the survey specifies.

One significant problem is the vast majority of the Tri-Valley's water supply -- about 80% -- comes from a state distribution system called the State Water Project. Zone 7, the water wholesaler for the Tri-Valley, doesn't have control over how much water the state sends, even during wet years.

DSRSD engineering services manager Dan McIntyre said indirect potable reuse could give local water agencies greater control over the region's water supply. During dry months, regional water agencies could have another source of drinking water, and excess water could be stored in the Livermore Valley's underground aquifer during wet months.

Researching the feasibility of toilet-to-tap is expected to cost about $500,000 -- to be shared among the region's water agencies -- and the actual cost will be determined when proposals are submitted later this spring, McIntyre said.

The process would consist of treating wastewater to drinking water standards through a specific filtration and disinfection process, then storing that water either in the underground aquifer or in Lake Del Valle, he said. The water would then be treated again when it is pumped into Zone 7 water treatment plants before it is sent to homes and businesses.

The proposed program would further treat such water through reverse osmosis or ozone filters, which brings the water up to drinking water standards, plus disinfecting with ultraviolet light, McIntyre said.

Doing such a process properly could require new infrastructure. DSRSD and the city of Livermore own reverse osmosis filters, but they haven't been used for 15 to 20 years, DSRSD operations manager Dan Gallagher said. Those facilities, along with a Zone 7 reverse osmosis filter that was active until a few years ago, could be upgraded and expanded.

The public survey, which polled 601 people who statistically represent the whole Tri-Valley, showed people were swayed to support toilet-to-tap when it was rebranded as "purified water" or when it was mentioned that astronauts and submarine crews drink reused, treated water, according to officials.

Indirect potable reuse would have additional treatment steps since the water would be put into a natural environmental barrier, Gallagher said.

If it's put into the underground aquifer, the water would trickle through many layers of soil before reaching the area where it is pumped back out to be sent to drinking water treatment plants. If it is sent to Lake Del Valle, it would mix with the lake water and would be treated again when it is pumped into drinking water plants.

One important distinction is indirect potable reuse is not the same as recycled water, Gallagher said.

Recycled water, such as the water that is distributed by DSRSD's residential recycled water program, is wastewater that is treated to remove solids and some impurities, but it does not meet drinking water standards and should only be used for irrigation or washing of hard surfaces.

But much of the water Tri-Valley residents drink now is unintentionally reused water, Olive said.

The region gets its water from Zone 7, and Zone 7 gets its water from the Sierra Nevada. But on its way to the Tri-Valley, the water from the Sierra snowpack gets used by northern cities like Sacramento, treated and dumped into the Delta, where it continues along -- being reused, treated and dumped several times through the process -- until it is deposited into Lake Del Valle.

He said the processes used by treatment plants cleans the water to drinking water standards with this reuse cycle in mind, and the proposed regional toilet-to-tap process would be a similar system.

"If you think about it, it's water that has received the treated effluent from Stockton," Olive said. "We're drinking the stuff right now, whether anybody wants to admit that or not."