Here's How Long That Teen Would Have to Pee in the Portland Reservoir to Make It Unsafe to Drink

The Slatest
Your News Companion by Ben Mathis-Lilley
April 17 2014 9:44 PM

Here's How Long That Teen Would Have to Pee in the Portland Reservoir to Make It Unsafe to Drink

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Calm down, Portland. You're going to be fine.

Photo by PORNCHAI KITTIWONGSAKUL/AFP/Getty Images

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.

Laura Helmuth Laura Helmuth

Laura Helmuth is Slate's science and health editor. 

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.

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Several smart people on Twitter quickly did the math and figured that a typical urination of about 1/8 gallon in a reservoir of 38 million gallons amounts to a concentration of 3 parts per billion. That’s billion with a b. For comparison, the Environmental Protection Agency’s limit for arsenic in drinking water—arsenic!—is 10 ppb.

The EPA doesn’t appear to have a limit for urine in drinking water, but it does limit nitrates in drinking water to 10,000 ppb, 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 3,333 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 2 percent of urine is nitrogen-rich urea. That means he’d have to urinate 166,666 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 21 seconds to urinate, that means he’d have to urinate constantly for 3,500,000 seconds, or about 40 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.

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