[Potassium as an indicator of anthropogenic contamination of swimming pool water]

Swimming pool water is processed, filtered and disinfected repeatedly in order to maintain hygienic conditions. Additionally, fresh water is added. However, it cannot be avoided, that the concentrations of certain components of swimming pool water will increase in the course of time. DIN 19,643 regulates that fresh water supply can be measured by nitrate concentration. Nitrate is mainly formed by oxidation of nitrogen containing organic compounds. Oxidation reactions are complex and the amount of nitrate formed by this process depends on specific factors which may vary in swimming pools with different technical equipment. Therefore nitrate is only of limited reliability to estimate fresh water addition in public swimming pools. Main sources for nitrogen containing compounds in pool water are sweat and urine which contain inorganic compounds like potassium. Potassium is a direct indicator of contamination. Its concentration is not influenced by chemical reactions because it is an inert compound. The urine release into the water of indoor pools was estimated by this parameter to be 77.5 ml/person, in outdoor pools about 60 ml. Potassium concentration in swimming pools will reach an equilibrium concentration, depending on the size of the pool, the number of bathers and the amount of fresh water added. This equilibrium concentration is mathematically calculated in a general approach. In none of 36 swimming pools where potassium concentration was measured, this calculated value was exceeded. The results indicate that the potassium concentration is a new valuable parameter to assess the quality of swimming pool water under hygienic aspects.