Pool Water Pathogens

by Nick Gromicko, CMI®
Germs from other swimmers and unsafe water supplies can easily contaminate pool water, especially if it isn’t properly disinfected. Contaminated recreational water can cause a variety of ailments and diseases, such as diarrhea, and skin, ear and upper respiratory infections, particularly if the swimmer's head is submerged.  Inspectors should be familiar with the problems caused by contaminated pool and spa water, and how to prevent them.
Children are common culprits in the spread of pathogens in pools. 

Viruses, bacteria and protozoa are the culprits in most swimming pool-related sickness outbreaks. The mucus, saliva, blood and skin of infected swimmers can directly contaminate pool and spa water with sufficient pathogens to cause infections in other swimmers who come in contact with it. Feces are a particular danger in pools, as the pathogens they contain are typically present in enormous numbers, approaching a million per gram of feces. A single fecal release in a pool could contaminate millions of gallons of water, according to the University of Arizona's College of Public Health.  Large outbreaks of disease are uncommon and they don’t typically happen in residential settings, but they should alert homeowners to just how contagious pathogens are when they’re waterborne. Consider the following such cases:

  • In 1998 in Georgia, 26 people were sickened after swimming in a pool with a child who had E. coli. Seven people were hospitalized and one was killed by the outbreak. The pool’s chlorine level had not been adequately maintained.
  • In New Mexico in 2008, a competitive swimmer who ignored symptoms of diarrhea caused 92 swimmers, including other competitive swimmers, coaches and lifeguards, to contract the illness.
  • In 2001 in an Illinois water park, 358 people contracted diarrhea, despite adequate chlorine and pH levels. Swimmers can add up to several pounds of feces per day in a typical water park.

Inspectors can benefit from learning the basic pathogens that are commonly found in swimming pools:

  • bacteria, such as E. coli, shigella (which causes dysentery), campylobacter and salmonella. Bacteria are generally killed quickly by chlorine disinfectant in properly maintained swimming pools at a concentration of 1 part per million. E. coli, for instance, will be inactivated in less than one minute if exposed to typical disinfectant concentrations;
  • protozoa, such as cryptosporidium (which causes diarrhea), and giardia, also known for its severe gastrointestinal effects. Some of these pathogens are highly resistant to chlorine and can survive for days in typical chlorine concentrations; andCryptosporidium is readily transmitted in pool water, and it's resistant to chlorine
  • hepatitis A and noroviruses.

Pool disinfectants can kill most germs in less than an hour, but for others it can take longer.  Cryptosporidium, for instance, can survive for up to 10 days in a properly chlorinated pool, and other pathogens are completely resistant to chlorine. In addition, the unique circulation patterns found in pools may allow poor water circulation in some areas, making it unlikely that all pathogen activity can be fully prevented. The unfortunate truth is that chlorinated swimming pools can and do transmit disease. Swimmers should not rely solely on the pool's chemical treatments, and should heed the following precautions:

  • Don’t ever swallow pool water. Children sometimes jokingly spit pool water back into the pool or at their friends, but this is dangerous, as some of it may be swallowed.
  • Shower with soap and water before and after swimming.
  • Wash your hands with soap and water after using a toilet or changing diapers.
  • Remove small children from pools for bathroom breaks and check diapers often.
  • Change diapers in a bathroom, not beside the pool.
  • Wash children, especially their rear ends, thoroughly with soap and water before they enter a pool.
  • Don’t swim when you have diarrhea. Diarrhea can be transmitted in pool water weeks after symptoms cease.
In summary, pathogens can easily permeate an entire pool.  Some are resistant to chlorination. Inspectors should advise their clients that chemical treatments for pools and spas are best supplemented with good hygiene.
Take InterNACHI's free, online "How to Inspect Pools and Spas" course.