How to Shock the Poop out of a Swimming Pool

BY Robert Lamb / POSTED June 28, 2010
Nooo!  (derfian/Creative Commons)

You know the scene from “Caddy Shack.” Someone throws a Baby Ruth candy bar into the pool and, mistaking it for what the Centers for Disease Control and Prevention (CDC) calls a “fecal incident,” everyone flees screaming like there’s a shark loose. Then we cut to a scene of men in full-body containment suits scrubbing every inch of a drained pool. Hilarity ensures.

Actual fecal incidents, however, are no joke. On any given weekend at your local pool, you’re just one toddler diaper away from dangerous recreational water illnesses (RWIs).  These are caused by organisms such as Cryptosporidium (aka Crypto), Giardia, E. coli and Shigella. We’re talking symptoms such as severe diarrhea. You might want to shed a few pounds at at the health club but THIS IS NOT THE WAY, PEOPLE.

There are two varieties of fecal incidents: formed fecal incidents and diarrheal fecal incident. I do not believe these need any explanation, other than a formed incident is far easier to clean up, and a diarrheal incident is a far riskier event as it will likely contain Crypto.

So if you’re suffering from diarrhea, please refrain from swimming.

As for cleaning up a fecal incident, one evidently cannot count on 1980s comedies for one’s understanding of proper pool maintenance. Naturally, draining a large pool, scrubbing it down and refilling it isn’t the best option, unless we’re talking catastrophic levels of nastiness in there. Just draining and refilling will typically take well over a day, and there’s also the whole cost of water to worry about.*

Instead, as my fellow sauna enthusiast informed me the other day at the Y, they “shock the pool.” Not being all that informed about pools (and being near-delirious from heat at that point), I imagined a member of the YMCA staff chucking a toaster into the water and listening on as a billion microbial voices suddenly cry out in terror and are suddenly silenced.

But no, shocking a pool (AKA super chlorination) involves cranking up the chlorine levels till all the microbial nasties perish. Once they’re dead, you let the chlorine level fall back down to swimmable levels. Then everyone jumps back in the pool (except maybe that one kid).

How long you shock the pool and how high a chlorine level depends entirely on the type of fecal incident. For instance, the CDC recommends a chlorine level of 3 parts per million for a period of 19 minutes in the event of a formed stool incident. That kills 99.9 percent of the Giardia. If it’s a diarrheal fecal incident, however, they recommend 40 parts per million for 6.5 hours.

If you want more info on this, have a look at this PDF from the CDC titled “Fecal Incident Response Recommendations: What Do You Do When You Find Poop in the Pool?” And the next time you show up at the pool for a swim and see the “routine maintenance” sign, thank your lucky stars that someone’s shocking the lanes for you.

* HSW’s own Matt Frederick informs me that, as of 2005, at least one country club still went the “Cadyshack” route of draining and scrubbing. Interesting…

About the author: Robert Lamb is a senior writer and podcaster at, where he co-hosts Stuff to Blow Your Mind with Julie Douglas. He has a love for monsters, an aversion to slugs and a hankering for electronic music.

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