Swim A Lot

Maintaining Pool Water

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 and ozone generated on site by passing an electrical discharge through oxygen or air. Chlorine may be supplied in the form of sodium hypochlorite solution, powdered calcium hypochlorite ("cal hypo"), cyanurated chlorine compounds (so called "stabilized" chlorine), or by dissolving chlorine gas directly 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 pool chemicals are used, it is very important to keep the pH of the pool in the range 7.2 to 7.6; higher pH drastically reduces the sanitizing power of the chlorine due to reduced ORP, while lower pH causes bather discomfort, especially to the eyes.

Where the water is sanitised by means of oxidisers, some suppliers of electronic monitoring equipment recommend that the efficacy of the oxidiser be measured by the oxidation-reduction potential of the water, a factor measured in millivolts, where the minimum acceptable ORP level in public pools is 650 millivolts. This is supposed to ensure a 1-second kill rate for microorganisms introduced into the water. Unfortunately, a commonly used non-chlorine supplemental oxidizer, potassium monopersulfate, can produce measured 650 mV levels even in the absence of all sanitizing residuals.

Cyanurated ("stabilized") chlorinators can give falsely high chlorine readings when tested with OTO (ortho-tolidene, a yellow indicator dye used in inexpensive test kits), since the chlorine indicated by the dye is mostly in a combined form instead of free, and does not contribute to ORP. ORP test cells are available as handheld instruments, and as probes for mounting permanently in the pool circulation plumbing to control automatic chlorine feeders.

Test kits to make basic meaurements of free chlorine and pH from a sample of pool water, which are the most important items to control in a swimming pool, are packaged with small dropper bottles of reagents. These reagents are typically OTO for chlorine and phenol red for pH. The kits include vials for mixing a water sample with the test reagents, and color charts for reading the indicated levels. Besides chlorine and pH, which should be checked frequently, more sophisticated reagent kits provide tests for acid demand and base demand, total alkalinity (TA), calcium hardness, and cyanurate ("stabilizer") concentration. These additional tests tend to vary only over weeks or months in a well-maintained pool, and thus need not be checked as frequently as chlorine and pH.

Pool sanitation, which necessarily involves toxic or mechanical means of killing microbes, can sometimes unintentionally irritate the swimmers, especially if poorly maintained, especially a too high level of chlorine and/or too low pH. Non-chlorine sanitizing chemicals and devices are promoted as being less harsh, but any sanitizer is harsh if overused, and proper levels of chlorine are not. Water circulating through a pipe can be sterilized with UV light instead of chemicals, but some level of chemical sanitizer is still needed, because only a small portion of the pool water passes through the circulation system at any given time, and the circulation system typically only runs for a few hours each day. UV sterilization also does not inhibit algae from growing on pool surfaces, and it does not break down dissolved nitrogenous nutrients that feed algae growth, so some type of oxidizing sanitizer is still needed to check these trends, although it need not be dosed during bathing hours for this purpose.

Generally, a well managed pool will have no smell or taste, be scrupulously clean, and have crystal clear water. Most people would not want to swim in a pool that appears dirty even if germs were under control. A pool pump circulates water through a strainer and filter to remove dirt and other suspended particles. The plumbing circuit may also include a gas or electric heater, solar panels, and chemical injectors.

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 it 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.

Chlorine may be generated on site, such as in saltwater pools . This type of system generates chlorine by electrolysis of dissolved salt (NaCl) using an electrical cell in the pool plumbing, instead of manually dosing the pool with chlorinating chemicals. Chlorine generators avoid the need for constant handling of sanitizing chemicals, and can generate sanitizing power at a lower cost than the equivalent chemicals, but they have a large up-front cost for the apparatus and for the initial loading of the pool with salt. The salt content gives the pool water a brackish taste, but not as salty as seawater. Pool water that splashes and evaporates, such as on a pool deck, leaves a salt residue. Being closer to isotonic salinity than fresh water, saltwater pools have an easier feel on the eyes, and a touch typically characterized as "silky", not unlike bath salts.

Text adapted from Wikipedia , the free encyclopedia under a copyleft GNU Free
Documentation License (GFDL) from the definition of " swimming pool"