Effect Measure

Accidents in swimming pools can be serious or fatal (drowning, broken necks) but fortunately they are rare. For pool operators one of the more likely nightmares of daily operation is when someone has “a fecal accident.” In other words, someone craps in the swimming pool. CDC has guidelines for chlorinated pools (which covers most public pools; they are guidelines because regulations are on the state, not federal, level). And they just revised them. It makes interesting reading, although I suppose this is an acquired taste. Here are the details, followed by a classic dramatic re-enactment on video.

In CDC’s world, fecal accidents come in two kinds (no, not designated number one and number two!). You have your “formed stool” accidents and your “diarrheal” accidents. Still with me? Good. The formed stool variety are not as bad. First, they are less likely to have pathogens and most of the bugs of all kinds are inside the formed stool, not on the surface. Second, intestinal pathogens can cause diarrhea and diarrheal discharge is much more likely to have pathogens in it. But pools are disinfected with chlorine, so the pathogens are killed, right? Pretty much. But different pathogens are more or less sensitive to disinfection by free chlorine. Inactivation of pathogens by chlorine depends on two factors: (i) the level, measured in chlorine concentrations in parts per million [ppm]; and the length of time the pathogen is exposed to that concentration. Usually the acidity or pH of the pool water affects this time/concentration combination, expressed as contact time (CT), the product of time in minutes and concentration in ppm. Required CT times for various pathogens are determined experimentally. E. coli is killed in about a minute at the recommended chlorine levels (1 part per million [ppm] at pH 7.5) but hepatitis A virus takes about 16 minutes. Some intestinal parasites like Giardia and Cryptosporidium have resistant forms that take much longer at the levels of chlorine found in pools: 45 minutes for Giardia and 15,300 minutes (almost 11 days) for Crypto (these numbers are for 99.9% or “three nines” inactivation). It is this last number, the three nines CT for Crypto, that prompted the revision. Experiments with a pathogenic isolate convinced CDC that the previous CT of 9600 was inadequate and needed to be bumped up to 15,300 (note that at 1 ppm a CT of 15,300 translates to 15,300 minutes of chlorine contact). So for Giardia and Crypto we are talking really long disinfectant times at 1 ppm. If you want to make sure the pool is safe from these guys you have to close the pool and ramp up the chlorine levels.

Close for how long? Ramp up how high? That’s where the formed stool and diarrheal distinction comes in. In 1999 CDC asked selected pool staff from around the country to collect (using a net) formed stool samples from some 300 fecal accidents from pools and waterparks in all parts of the US. They found Giardia in 4.4% but Crypto in none of them. So a formed stool accident is unlikely to exposed other bathers to Crypto. Diarrheal discharges may have Crypto in them, however, so CDC recommends much more stringent disinfection guidelines. In either case the pool operator should try to remove the offending material (trying not to break it into pieces in the case of formed stool) after first making everyone leave the pool and any pool connected to it and using the same filter. For a formed stool accident, the chlorine is raised to 2 ppm (pH 7.2 – 7.5) and kept there for a half hour. Unfortunately the problem for a diarrheal accident is much tougher. The chlorine should be jacked up to 20 ppm and kept there for 8 hours. That’s a “come back tomorrow folks” situation. Since this is a very high chlorine level and some test kits can’t handle it, lower levels may be used but must be continued for longer. The required times are easy to calculate from the CT numbers. In either case a record should be kept in a fecal accident log.

Fecal accidents in pools have received their share of attention from Hollywood. Here is a dramatization from the cinema classic, Caddyshack. Enjoy:


  1. #1 Paul Schofield
    February 18, 2008

    I used to work in a British public swimming pool (run by the council) and we had pretty much similar guidelines. And had to apply them at least once every other week. It was a reasonably small pool, so the water cycled through at a reasonable rate, cutting some of the wait times (although obviously not all that much).

    Of course, that relies on the fecal matter being in the pool. Not at the top of the water slide.

    How they managed that one I never worked out.

  2. #2 M. Randolph Kruger
    February 18, 2008

    You know Revere I always wondered about the snot wads too when I was a life guard. You would see people clearing their bowels in the kiddie pool all the time. Separate system. All the while 12 feet away someone would dive in, get held under playing and then snork water into that very clean sinus (right) and then come up and blow yesterdays pollution out from down near their assholes thru their sinuses and nose.

    Crap is crap…How bout that stuff that you would swim thru unseen for the better part until someone screams there’s a big Bogie in some chicks hair?

  3. #3 victoria
    February 19, 2008

    The last time I went swimming in a public pool was 1999. Swam into two floaties. Vomited for a week. This is a revolting topic. Congratulations!

  4. #4 pauls lane
    February 19, 2008

    I don’t do pools (public or private) or hot tubs. I don’t even like a bath. Hot shower is the way to go. Skinny dipping in the ocean is also great.

  5. #5 jen_m
    February 19, 2008

    I more or less quit swimming in public pools right around the time I first read the last CDC guidelines for public pools, when it dawned on me that there was probably a lot of fecal contamination from unclean behinds even absent stool release.

    Victoria’s right. This topic makes me shudder.

  6. #6 Brian X
    February 19, 2008

    Hm. Oddly enough, it reminds me of the microbiological distinction between steak and hamburger, in a way.

    And then of course you have the “egg drop soup” problem in hot tubs — not usually a sanitary hazard, but pretty disgusting.

  7. #7 victoria
    February 20, 2008

    If one goes swimming in the sea, by a seaside city like; Sydney, Manila, San Fransisco, Rio de Janeiro, Miami etc, there are usually hundreds of bobbing floats. Crap as far as your eye can see.

  8. #8 M. Randolph Kruger
    February 20, 2008

    You wont see it off of Miami. Nor San Francisco. Now that medical waste, thats a different story. We keep our floaters in the treatment plants and discharge “treated” water and the solids are sold to farmers after retreatment. Still has the heavy metals though. Of course now off of New Orleans that treated water has created a permanent oxygen robbing environment. The oyster and crab people call it the “dead zone”

    If there is a floatie around those cities in the US then they were put there locally and not thru the sewage treatments.

  9. #9 victoria
    February 20, 2008


    Victoria here.

    A floatie is a floatie. It does not matter where it comes from. Yes, there are treatment plants, however floaties always find a way. They are every where.

  10. #10 no thanks
    February 20, 2008

    At risk of sounding terribly crass, some of that was actually funny.

    Seriously though, people need to start taking poo more seriously. Not just poo in the pool, but in the food supply, and handwashing after using the loo (and all the other usual times & places), and cleansing their bottoms more thoroughly (yes, also wash down there when you shower), and all of it.

    The casual disregard of hygiene that has marked the past 60 or so years is a product of ubiquitous working antibiotics. The more we see resistant bugs, the more people are going to realise that the old expression “eat s— and die” was literally true.

  11. #11 victoria
    February 20, 2008

    no thanks – you have to be a fellow Australian with that sense of humour.

  12. #12 Neil Wilkinson
    February 20, 2008

    “eat shit and…….?”

    lose all your friends?

  13. #13 AnnieRN
    February 22, 2008

    I remember going to summer camp in northern Michigan when I was a kid. One of the staff members had a St. Bernard who was kept tied down by the lake. Within a few days, there were big ol’ St. Bernard-sized thingies floating in the swimming area. Kept me out of the water better than any “Jaws” scenario. Ew, ew, ew, ew, ew. Thanks for the memory jolt. AnnieRN

  14. #14 swimming pool designs
    May 11, 2009

    Swimming pool accidents are always serious not sometimes, Every year the no. of accidents are getting up which is really bad.
    I remember, Last year a famous singer “Ishmeet Singh” is also found dead in a swimming pool. When we came to know, we were shocked.
    Be careful guys and follow the rules.
    thanks for sharing such a good post. cheers.

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