Water use in data centers depends heavily on whether the cooling system reuses water or consumes water during heat rejection.
In a closed-loop system, water or coolant circulates through pipes and equipment repeatedly. The fluid absorbs heat inside the facility and carries it to equipment that rejects the heat.
Because the same fluid is reused, water consumption is usually much lower than systems that rely on evaporation.
In an open-loop or evaporative system, water is exposed to air and some of it evaporates as part of the cooling process. This can reduce electricity use for cooling, but it can increase water consumption.
These systems are not automatically bad, but they require careful local review.
Closed-loop: generally lower ongoing consumption.
Open-loop: can consume more due to evaporation.
Closed-loop: may use more mechanical cooling depending on design.
Open-loop: can be more electrically efficient in some climates.
Closed-loop: water-sensitive areas or predictable low-water designs.
Open-loop: areas where water availability and policy support it.