How dangerous is pee?

Laura Helmuth, Slate's science and health editor, has an article about some obscure math:

Oh, Portland. A teenager urinated into one of the city’s drinking water reservoirs the other day. That’s gross, sure, and aggravating; what a brat! But in one of the most spectacularly stupid decisions in years, the city is going to drain the reservoir. The most spectacularly stupid decision in about three years, anyway; if this sounds familiar, that’s because Portland did the same thing in 2011.
The decision seems to be based on some combination of chemophobia, homeopathy, and pee shame. The dose makes the poison, and clearly this dose is negligible. But is it possible to calculate precisely how illogical Portland’s decision is? Let’s try to put some numbers on it.
Several smart people quickly did the math and figured that a typical urination of about an eighth of a gallon in a reservoir of 38 million gallons amounts to a concentration of three parts per billion. That’s billion with a b. For comparison, the Environmental Protection Agency’s limit for arsenic in drinking water— arsenic!— is ten parts per billion.
The EPA doesn’t appear to have a limit for urine in drinking water, but it does limit nitrates in drinking water to ten thousand parts per billion, and urine does contain a lot of nitrogen, so let’s use that as a proxy.
How many times would that teenager have to pee in a Portland reservoir to produce a urine concentration approaching the EPA’s limit for nitrates in drinking water? About four thousand times.
But, of course, urine is 95 percent water. (If you’re ever trapped in rubble after a natural disaster, go ahead and drink it.) Only about two percent of urine is nitrogen-rich urea. That means he’d have to urinate over a hundred and sixty thousand times for the concentration of urea to approach that of the EPA’s limit for nitrates in drinking water.
Since most animals, including idiot teenaged show-offs, take about twenty seconds to urinate, that means he’d have to urinate constantly for three and a half million seconds, or about forty days. Hopefully, he’d have friends constantly supplying him with tasty Portland microbrews.
Needless to say, this doesn’t take into account the fact that the resulting 1.3 million gallons of urine, which again is 95 percent water, would raise the volume of the reservoir. So add another day or two of peeing to really make the water unsafe to drink.
Draining the reservoir is paranoid, illogical, and expensive. But the most frustrating thing to me about the whole episode is that there is actually something Portland could do to its water supply that would have an immediate, positive, and repeatedly scientifically validated impact on public health: add fluoride. Paranoia is not healthy.

Rico says the good people of Portland should sue the city for this stupidity...