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.
Reusing the same fluid reduces losses inside the loop, but it does not by itself determine site water consumption. A closed chilled-water loop can still reject heat through an evaporative cooling tower outside.
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: loop losses may be low, but total site water use depends on the final heat-rejection equipment.
Open-loop: can consume more due to evaporation.
Dry heat rejection: can require more mechanical energy in hot conditions depending on design.
Open-loop: can be more electrically efficient in some climates.
Dry heat rejection: often favored where minimizing process-water consumption is a priority.
Open-loop: areas where water availability and policy support it.