SAN FRANCICO (KCBS)— San Francisco city officials say you won’t notice a thing when they start mixing groundwater into the pristine Hetch Hetchy water supply. The plan is to try and boost reserves by pumping millions of gallons of groundwater a day.

The blending is expected to begin in late 2016 and the San Francisco Public Utilities Commission (SFPUC) has started digging in and around Golden Gate Park in search of water flows with plans to pump up to four million gallons a day to blend into the supply.

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Groundwater is not as appealing in taste or as pure, but the SFPUC’s groundwater project manager Jeff Gilman said it’s clean enough and that it won’t be that much, up to 15 percent, groundwater in the blend.

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“People are not currently drinking pure Hetch Hetchy. They’re drinking a blend and we’re just taking another small step, blending, trying to maximize our local resources,” Gilman said.

Taste tests show people prefer the pure Hetch Hetchy supply, but it’s not just the taste. While some of the calcium and sodium in the groundwater is harmless, tests have shown there are nitrates that come from fertilizers and sewage pipes in the dirt that exceed state standards.

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City officials said they’ll treat the groundwater by diluting it so the nitrates are reduced to safe levels. They’ll also use chlorine to kill off any pathogens that could potentially cause illness.