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