As temperatures rise, the San Antonio Water System is inadvertently providing an old-fashioned method for cooling off.

It is opening hydrants across the South Side and parts of northern Atascosa County this week, flushing water lines while it adds Edwards Aquifer water to the Medina Lake water in those areas and changes the type of disinfection used.

Millions of gallons of water will be released from 350 to 375 of the 500 hydrants in the area, SAWS staff said. Each hydrant will flow from five to 20 minutes.

Because the water is clean, residents are urged to capture it for their own use, as some customers have done in the past, or simply enjoy the stream running down the road, SAWS spokeswoman Anne Hayden said.

The water can be up to 4 inches deep along the curb.

The flushing is needed because the quality of the water in the storage tanks in the two areas is starting to decline as the water heats up with the weather, Hayden said.

Although the water meets all drinking-water standards, Hayden said SAWS wanted to switch the water source before water quality became an issue. The system will most likely switch back to Medina Lake water exclusively in a month, she said.

Some residents might be unhappy with what they see as a waste of water. But “while conservation is a prime concern,” Hayden said, “water quality and safety for the customer and following state regulations is the top priority.”

Because the water comes from Medina Lake, it has bits of organic matter that can render it undrinkable if allowed to sit too long in a storage tank or pipe, Hayden said. By changing the type of chlorine that is used and adding water from the Edwards, which does not have organics, the matter in the water can be killed and flushed out.

How large an effect the additional pumping from the Edwards will have on the level of the aquifer is not known. SAWS crews do not know how much water it will take to clear all the lines, so the exact amount of water to be released and replaced is not known.

Although SAWS will be sending water down the street, all conservation rules will still be in place and enforced.

The tanks and water system are in former service areas of the Bexar Metropolitan Water District, which did the same flushing last year.

“While SAWS customers in this limited area may notice a temporary change in the taste or smell of their drinking water, we want to assure everyone that the water will continue to be safe to drink,” said Steve Clouse, SAWS chief operating officer and senior vice president.

Because the disinfection method for water from Medina Lake is different from that for water from the aquifer, SAWS is telling medical facilities and dialysis centers to adjust their treatments. People with fish tanks might also need to change how they treat the water for the tanks.

A meeting to inform residents about why the flushing is occurring will be Thursday at 6:30 p.m. at the Cortez Library at 2803 Hunter Blvd. A second meeting will be held next week. More information is available by calling 210-922-1221 or visiting