Chlorine and other disinfectants do indeed help to clean the water, but some germs can survive in even the best-kept pool. For example, cryptosporidium may live in pool water for several days. Crypto causes a diarrheal illness and may rinse off the bodies of infected people or diapered children into the pool. If you swallow infected pool water, you may become sick.

Other germs may live for a few minutes or a few hours in a chlorinated pool: Giardia, Shigella, and E. Coli may cause diarrheal illnesses. Pseudomonas Aeruginosa may cause an ear infection called swimmer's ear and also a skin infection called "hot tub rash," that is usually associated with very warm pools and spas.

While keeping the correct chlorine and ph levels will minimize water-borne illness, prevention is also a good idea. Keep diapered children in the water for only brief periods and keep sick people out of the water altogether. And, don't ever swallow pool water.