Amazon Strategized About Keeping Its Datacenters Full Water Use Secret

Adding heat to local water and returning it after one pass is the minimalist use of water. Usually there is little need for additives, like chlorine to kill bacteria. A lot depends on the water purity. Water with suspended food = chlorine to suppress assorted growths. This heat the water and can harm the ecology - depends on the volume/added heat. Often filtering is needed with algae etc and a small river plus large heat can damage the downstream ecology. Water is used because it is 'free' - a potentially false economy. Lakes are more tolerant, but not immune - depends on volume. Best use is water to cool in a closed system coupled with air forced radiators - these need additives for growth suppression and corrosion inhibition. This method does not use evaporative cooling, so it is less capable, but a sealed non contaminating system can be made. Most nuclear power uses evaporative cooling towers that evaporate large water volumes and must be treated for algae/bacteria/legionnaires disease and they must add fresh water and create toxic waste water that must be treated. It is a grubby business. Best is a pure air based heat dump, which is the higher cost as long as enough local air is added so the local environment is minimally affected. I expect local rules will be enacted to mitigate these effects