Abstract

The swimming pool market has grown at an average of ~3%/year over the last 10 years. The total number of pools in 1991 was ~6 × 10⁶ in the United States. The number of spas and hot tubs has grown rapidly since 1970, with an estimated 2.7 × 10⁶ spas and hot tubs in 1991 in the United States in a growing market. Most swimming pools are of the recirculating type. Through filtration, chemical treatment, and dilution with rain and makeup water, the water can be reused without draining and refilling. Sanitizing chemicals must be added regularly to oxidize pool contaminants and kill and control disease-carrying bacteria and other organisms introduced by swimmers and dirt entering the water. It also is necessary to destroy algae whose spores are carried into the water by wind and rain. The pH of pool water must be maintained within a desirable range for swimmer comfort and optimal effectiveness of chlorine sanitizers. In order to control the corrosive or scaling tendencies of pool water, it also is necessary to maintain a proper balance between pH, alkalinity, and hardness. Undesirable trace metals such as iron, manganese, or copper are sometimes found in source water or formed by corrosion of pool equipment. Unless removed, these metals discolor pool water and cause stains, especially damaging to plaster pool surfaces. Filtration of pool water is necessary for removal of suspended solids which otherwise cloud water and interfere with the disinfection process.