The US city of Portland, Oregon, is ditching 38 million gallons of drinking water from a reservoir after a teenager was caught on camera urinating into it, officials said Thursday.

The water -- enough to fill nearly 60 Olympic-size swimming pools, according to reports -- will be discarded despite tests finding no evidence of contamination.

The 19-year old man, seen with two friends carrying skateboards in the early hours Wednesday, was filmed urinating through an iron fence into the reservoir in southeast Portland shortly after 1:00 am.

David Shaff, Portland Water Bureau Administrator, said about 38 million gallons will be discarded and replaced with fresh water from the Bull Run water supply -- even though subsequent tests showed no contamination.

"Our customers have an expectation that their water is not deliberately contaminated. We have the ability to meet that expectation while minimizing public health concerns," he said.

Portland Water Bureau spokesman Tim Hall dismissed suggestions that flushing away so much water was an overreaction to one man urinating in a reservoir.

"Any time there is human contamination of our drinking water, as a precaution we shut the reservoir down and begin to drain and clean it," he told AFP.

He added: "We're in an enviable position of having an abundant supply ... Therefore releasing this water did not create any financial impact in the city or for our customers."

But the decision raised eyebrows further south down the US West Coast, where California is suffering from its worst drought in decades.

"Really, Portland Water Bureau officials, do you have to flush 38 million gallons of potable water for the sake of a cup or two of human urine?" one Los Angeles Times commentary asked.

"Have a little pity on your neighbors to the south. Remember California? That big, dry behemoth .... How do you think we feel, when we hear the whoosh of 38 million gallons going to waste?

"We're in a drought, remember? Not good. No, not good at all."

The three men involved have been excluded from the reservoir area, while police were reviewing the video surveillance footage to decide whether to press criminal charges, Hall said.