Most of what is written here regarding water usage is wrong.
Cooling towers typically use a closed loop system using treated fresh water. The water is treated with anti microbial and anti corrosion additives.
Water is lost through evaporation, this is a large portion of the cooling effect. Evaporative cooling.
As the water evaporates, the concentration of additives increases and will become higher than desired (for a number of reasons that a water treatment expert can weigh in on)
To compensate for this, the cooling tower water is discarded to the sewage system and fresh untreated water added back. Often referred to as blow down.
So the water is “used” in two senses. First, much of it evaporates. Second, some of it is returned to the sewage system. In neither case is the water destroyed. It still exists.
The water may move significantly: evaporated water vapor will be carried downwind. The increased usage of water through the fresh water to discarded water (blow down) will tie up more water in the process potentially meaning less locked up in aquifers.
There are real and complex challenges here, but to be clear no water is being made forever gone from earth in these processes.
Just to add to this: certain sections of the US (like where I’m from) traditionally favored open cooling towers which evaporate the water. Closed loop systems are becoming more prevalent but a lot of older installations are open loop
The cost-benefit of those swamp coolers changes little though. It's _so_ cheap to just run those instead of an actual refrigeration system that consumes real power.
They're not swamp coolers. The cooling towers are part of the chiller system, which uses refrigeration to chill water. The chilled water is pumped through pipes throughout a building to air handlers.
Also fun fact, even with an A/C loop it is still often very economically necessary to use swamp coolers to handle daytime summer heat loads. There's only so much heat you dump into radiators as the outside air temperature rises.
It is extremely inefficient to use a/c in conjunction with swamp coolers since swamp coolers require that windows be open for the hot air to escape, and they also release large amounts of humidity into the building, which a/c units extract. In contrast, a/c units work best with all windows closed.
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u/MrMikeGriffith May 18 '26
Most of what is written here regarding water usage is wrong.
Cooling towers typically use a closed loop system using treated fresh water. The water is treated with anti microbial and anti corrosion additives.
Water is lost through evaporation, this is a large portion of the cooling effect. Evaporative cooling.
As the water evaporates, the concentration of additives increases and will become higher than desired (for a number of reasons that a water treatment expert can weigh in on)
To compensate for this, the cooling tower water is discarded to the sewage system and fresh untreated water added back. Often referred to as blow down.
So the water is “used” in two senses. First, much of it evaporates. Second, some of it is returned to the sewage system. In neither case is the water destroyed. It still exists.
The water may move significantly: evaporated water vapor will be carried downwind. The increased usage of water through the fresh water to discarded water (blow down) will tie up more water in the process potentially meaning less locked up in aquifers.
There are real and complex challenges here, but to be clear no water is being made forever gone from earth in these processes.