Water disinfection for purity

Water cleanliness and disinfection

Swimming pool water must be maintained with very low levels of bacteria and viruses to prevent the spread of diseases and pathogens between users. Strong oxidising agents are often used, especially simple chlorine compounds such as sodium hypochlorite. Other disinfectants include bromine compounds (very rare) and ozone generated on site by passing an electrical discharge through oxygen or air. When chlorine products are used, these can be in the form of hypochlorite solutions and by dissolving chlorine gas in water. Maintaining a safe concentration of disinfectant is critically important in assuring the safety and health of swimming pool users. When any of these chemicals is used, it is very important to keep the pH of the pool within a certain range (7 to 8), because either acid or alkali can cause chlorine gas to be produced. This is especially important in installations using chlorine gas itself because the reaction with water produces hypochlorous acid and hydrochloric acid which would make the water dangerously acidic if not neutralised.

In all cases where the water is sanitised by means of oxidisers, the efficacy of the oxidiser is measured by the oxidation-reduction potential of the water, a factor measured in millivolts, where the minimum acceptable ORP level is 650 millivolts. This is thought to ensure a 1-second kill rate for microorganisms introduced into the water.

The proper management of a backyard swimming pool can be a difficult and time-consuming task. The chemical balance of the water has to be carefully monitored to make sure that is not become fouled with algae or bacteria. Either of these will make the water smell and look unpleasant and can be a serious health hazard. The water must also be kept clear of debris such as fallen leaves and sticks, as these encourage fouling and become very slippery and dangerous as they start to decompose. Most people keep their pool either covered over or drained entirely during the months of the year in which it is not in use, as this is the easiest way to keep it sanitary (draining however can be a serious safety hazard with deeper pools and re-filling can be fairly expensive in areas where water is scarce). Public and competitive swimming pools are therefore often, especially in colder climates, indoor pools—covered with a roof and heated—to enable their use all year round.