An average size dog is equal to three humans in terms of the stuff they will bring along with them into a pool. If you have more than one dog in the pool, multiply that number by three and you will soon learn why you are using more sanitizer or chlorine than normal. The fact is, a dog will introduce fecal matter to the pool pretty regularly, along with insects, body oils, dirt, and who knows what else. This is especially true if they are primarily outside dogs. Animals always have small particles of fecal matter stuck in their fur. This fecal matter will contaminate the pool’s water, potentially aiding in the transmission of Recreational Water Illnesses (RWI’s), such as E. coli, Giardia, Hepatitis A, and Cryptosporidium.
If you think that you and your kids never ingest any of that pool water, guess again. Those ‘external additives’ will raise pH more quickly and consume free available chlorine rapidly. 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, skin, ear, and upper respiratory infections, particularly if the swimmer’s head is submerged. Large outbreaks of disease are rare and they don’t typically happen in residential settings, but homeowners should be aware of just how contagious pathogens are when they are waterborne.