RWIs are caused by germs like "Crypto" (KRIP-toe, short for Cryptosporidlum), Giardia (gee-ARE-dee-uh), E. coli 0l5:H7, and Shigella (Shi-GE-luh) and are spread by accidentally swallowing water that has been contaminated with fecal matter. How does a pool get contaminated? You share the water with everyone in the pool. If someone with diarrhea contaminates the water, swallowing the water can make you sick.
The great news is that germs causing RWIs are killed by chlorine. However, chlorine doesn't work right away. It takes time to kill germs and some germs like "Crypto" are resistant to chlorine and can lie in pools for days. That is why even the best maintained pools can spread illness. Therefore, Healthy Swimming behaviors are needed to protect you and your kids from RWIs and will help stop germs from getting in the pool in the first place. Here are six "P-L-E-As" that promote Healthy Swimming:
PLEASE don't swim when you have diarrhea
http://accesswdun.com/article/2002/4/195921