SAN FRANCISCO (KPIX 5) — New information surfaced Thursday about what has been causing stinky water to come out of some Bay Area taps since last week.

People in San Francisco and Palo Alto have been complaining their water smelled and tasted bad.

The source of the foul smelling and tasting water that was revealed by water officials Thursday was a different explanation than the one given earlier this week.

On Monday, the SFPUC told KPIX 5 it was because they started pulling water from the San Antonio reservoir, which stirred up some naturally occurring sediment in pipes that hadn’t been used in a while.

However, on Thursday the Public Utilities Commission said the problem was due to algae, r rather a byproduct of that algae called geosmin.

It’s clear to customers that something is different about the water in San Francisco and parts of the Peninsula.

Last week, people began complaining on social media that the water “smells like a swamp” and was “creating a burning sensation on the sides of the tongue.”

The water was even being blamed for diarrhea and stomach issues.

To demonstrate the water is safe to drink, the San Francisco Public Utility Commission Assistant General Manager of the Water Enterprise Steven Ritchie took a swig of what he said was San Francisco tap water in front of a room full of reporters

“If you’d like, there is water to share here,” said Ritchie. “I’m happy to have it myself.”

He admitted that even folks at the PUC noticed a change in the taste, but insisted it is safe to drink.

The agency says they manually test the water over 100 times each day at different locations for things like pathogens, bacteria and minerals.

On Wednesday, those tests revealed a byproduct of algae called geosmin at the Sunol Valley Treatment Plant.

They believe came from algae at the San Antonio Reservoir though they have not yet found any blooms.

As for those reporting health issues?

“There is no clinical evidence that geosmin causes any health effects,” said Ritchie.

He said it is a naturally occurring and commonly found compound in many other water systems, though it’s not common in the Hetch Hetchy.

They’re not sure what caused it, but they have stopped taking water from the San Antonio Reservoir today and are ramping down the affected treatment plant

“With these measures, we believe the taste and odor issues will begin to dissipate,” said Ritchie.

How soon that happens will largely depend on how quickly the water moves through the system. Officials hope people will notice changes within a week.

There does seem to be a discrepancy in complaints, with many issues coming from the same few neighborhoods, while others say they haven’t noticed a change.

The agency explained the water generally moves through the lower elevations first. A map of the city illustrated a sort of ring around San Francisco where most of the complaints are coming from.

The higher elevations will take longer to notice an agent.

We asked to see the water test results and the agency has agreed to make those public.

When asked why the SFPUC changed their answer about the cause of the different smell and taste and why it took so long to figure out it was due to algae, officials said this is not a common time of year for algae, so it wasn’t intuitive at first that algae would be the cause.

They added it is very common to experience changes in water taste and smell when the utility activates a new reservoir due to sediment.

After complaints continued, they increase their testing and found the algae byproduct.

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