Because of the many different water contaminates that can be present water treatment chemicals are necessary. One of the most important factors in the treatment of swimming pool water is to ensure that it is clean, safe and free from disease causing germs. For these reasons chemicals that are classified as sanitizers or disinfectants are used. One of the most popular and well-known sanitizers for disinfection of swimming pool water is chlorine.
Humans - We carry a lot of stuff on our own bodies that can contaminate water. Every time we enter the water our bodies shed millions of bacteria. One person can exude 3 pints of perspiration in a spa in one hour. Through fecal contamination humans can introduce disease-causing bacteria such as e-coli or parasites like cryptosporidium. Deodorants, hairspray, body lotions and perfumes can also add to water quality demands.
Weather - Rain can wash dirt, smog and silt into the pool. Acid rain can wreak havoc on the water balance and cause metal ions to precipitate. Windstorms can blow in materials that cause contamination. The sun causes evaporation. The evaporation rate of a swimming pool in Southern California is approximately 6 to 8 feet per year. That is equal to the depth of an average backyard pool being emptied in one year.
Polluted Air - Chemical or bacteria that is airborne. A typical air blower on a spa will pump 50 cubic feet of air every minute into the water. Also, pools with fountains or airing devices. When air passes through water it leaves behind any pollutants it contains. Water acts as a natural filter to whatever is in the air, car exhaust, dust etc.
Trace Metal Oxides - Iron, manganese, cobalt and copper are just a few types of metal ions that can cause staining on pool and spa surfaces.
Dissolved Solids - These include salts, chemicals leached from the soil, sulfer, calcium and phosphates etc.
Un-dissolved Solids - Small particles of dirt, dust, pollen or floating alge.