How often do they change pool water completely?

Typically, pools are not drained completely unless there are major renovations or maintenance demands. There simply is no need to do that. Fresh water is added to the pools - either manually or through an auto-fill system - either directly into the pool or in the pump room. Water is loosed through evaporation, pool activities and routine cleaning of the filtration system (backwashing). Occasionally, fresh water will need to be added (after pool water is "dumped") because of an extreme chemical imbalance. In this case, the pool should be closed and you probably will not know about it. There is a number of reasons pool water turns "white cloudy" (low turbidity). Improper filtration, insufficient water circulation or flow rate, poor water chemistry, wind, rain, vegetation, dry skin flakes, cosmetics and hair products from swimmers are among the many factors that need to be examined. In short, cloudy water is the result of microscopic suspended particles. Determining the contributing factor will yield the proper remedy. If the pool water turn colors like blue-green or red-brown, then you have a more serious condition and should have an expert examine the situation. Pool water temps. in relation to air temp.: The most ideal is to have the air temp 5 degrees warmer than the water. This is not always possible. At a minimum, air flow/ventilation is absolutely necessary. Recreational water illnesses are caused by cryptosporidium (parasite), Giardia (parasite), E. coli (bacteria) and shigella. When people infected with these diseases have a fecal release in the water and there is insufficient disinfectant (most often Cl) to inactivate the pathogen, then swimmers who ingest water, will swallow some of those germs and will become ill. Crypto can remain active at normal disinfectant levels for several days (6 -7 days). Protozoa are resistant to chlorination in swimming pool water. Therefore, remedies for total disinfection are to raise the Cl (or sanitizer) level to an unsafe swimming level and allow the pool water to turn over (filter) and return to an accepted level. The flow rate (turnover rate) at your pool will determine the length of time this process will take. In most areas, at a minimum, the Health Department regulates pools by taking weekly water samples and yearly visits. If there is a problem cited or water tests reveal a potential hazard, the Health Department is obligated to intervene and possibly fine ($$) or close a pool until the problem(s) are resolved. that's my :2cents: -mermaid- CPO PA Dept. of Agriculture, Certified Commercial Pesticide Applicator Registered Public Bathing Place Manager Mermaid pretty much hit the nail on the head. For drinking water (and pool water too) especially from a surface water supply the danger of infection comes from "turbidity." Pathogens can attach themselves and "hide" from disinfectants, if the water is unfiltered and remains turbid. A healthy immune system also helps, as the first people to suffer are most often those with compromised immune systems (very old, very young, and others with illnesses impacting the immune system). Turbid appearing water can often result from air bubbles in the filter system (this isn't turbidity, but it is hard to tell the difference), so cloudiness in a pool or glass of water can be misleading. There are standard methods (lab procedures) for testing turbidity in water, so one can't always tell by looking at it. As Mermaid indicated, "Recreational water illnesses are caused by cryptosporidium (parasite), Giardia (parasite), E. coli (bacteria) and shigella" and these aren't always killed by chlorination. They can be present in OW bodies, especially after storm events producing runoff, and originate from animal *** (yes, bears do poop in the woods).

Typically, pools are not drained completely unless there are major renovations or maintenance demands. There simply is no need to do that. Fresh water is added to the pools - either manually or through an auto-fill system - either directly into the pool or in the pump room. Water is loosed through evaporation, pool activities and routine cleaning of the filtration system (backwashing). Occasionally, fresh water will need to be added (after pool water is "dumped") because of an extreme chemical imbalance. In this case, the pool should be closed and you probably will not know about it. There is a number of reasons pool water turns "white cloudy" (low turbidity). Improper filtration, insufficient water circulation or flow rate, poor water chemistry, wind, rain, vegetation, dry skin flakes, cosmetics and hair products from swimmers are among the many factors that need to be examined. In short, cloudy water is the result of microscopic suspended particles. Determining the contributing factor will yield the proper remedy. If the pool water turn colors like blue-green or red-brown, then you have a more serious condition and should have an expert examine the situation. Pool water temps. in relation to air temp.: The most ideal is to have the air temp 5 degrees warmer than the water. This is not always possible. At a minimum, air flow/ventilation is absolutely necessary. Recreational water illnesses are caused by cryptosporidium (parasite), Giardia (parasite), E. coli (bacteria) and shigella. When people infected with these diseases have a fecal release in the water and there is insufficient disinfectant (most often Cl) to inactivate the pathogen, then swimmers who ingest water, will swallow some of those germs and will become ill. Crypto can remain active at normal disinfectant levels for several days (6 -7 days). Protozoa are resistant to chlorination in swimming pool water. Therefore, remedies for total disinfection are to raise the Cl (or sanitizer) level to an unsafe swimming level and allow the pool water to turn over (filter) and return to an accepted level. The flow rate (turnover rate) at your pool will determine the length of time this process will take. In most areas, at a minimum, the Health Department regulates pools by taking weekly water samples and yearly visits. If there is a problem cited or water tests reveal a potential hazard, the Health Department is obligated to intervene and possibly fine ($$) or close a pool until the problem(s) are resolved. that's my :2cents: -mermaid- CPO PA Dept. of Agriculture, Certified Commercial Pesticide Applicator Registered Public Bathing Place Manager Mermaid pretty much hit the nail on the head. For drinking water (and pool water too) especially from a surface water supply the danger of infection comes from "turbidity." Pathogens can attach themselves and "hide" from disinfectants, if the water is unfiltered and remains turbid. A healthy immune system also helps, as the first people to suffer are most often those with compromised immune systems (very old, very young, and others with illnesses impacting the immune system). Turbid appearing water can often result from air bubbles in the filter system (this isn't turbidity, but it is hard to tell the difference), so cloudiness in a pool or glass of water can be misleading. There are standard methods (lab procedures) for testing turbidity in water, so one can't always tell by looking at it. As Mermaid indicated, "Recreational water illnesses are caused by cryptosporidium (parasite), Giardia (parasite), E. coli (bacteria) and shigella" and these aren't always killed by chlorination. They can be present in OW bodies, especially after storm events producing runoff, and originate from animal *** (yes, bears do poop in the woods).