Almost none of them run closed loop systems. They’re extremely expensive, and even if they did they actually still use just as much water, it’s just that the water is now being spent at a gas or coal power plant instead of on site due to the increased energy usage.

The systems that most data centers use are called adiabatic cooling systems. They evaporate water after a closed loop because the problem isn’t moving the heat away from the servers, it’s getting rid of them fast enough.

Conveniently most data center providers provide absolutely no statistics about these things because they look very bad to the public, but researchers have calculated usage.

https://datacenters.microsoft.com/wp-content/uploads/2023/05/Azure_Modern-Datacenter-Cooling_Infographic.pdf

https://www.washingtonpost.com/technology/2024/09/18/energy-ai-use-electricity-water-data-centers/

https://www.eesi.org/articles/view/data-centers-and-water-consumption

They use evaporative cooling on the AC that actually cools the inside of the data center. Evaporating water cools things down significantly more than simply splashing cold water at them.

This significantly reduces their costs on electricity because AC runs much more efficiently when the condenser side is cool.

They do not (usually) use evaporative cooling on the GPUs themselves. Evaporative cooling is used more directly too, but the indirect variant is better because it doesn't raise the humidity inside the data center. This is why so many data centers are being built in deserts now (well this and the cheap land).

When they do use it without the heat pump/AC in tandem, then it means pushing hot air through a water soaked membrane, not using all that water in the coolant pipes for the servers. The closed loop is still closed, the evaporation happens outside of the loop.

An interesting guess in a capitalist dystopia.

The answer is: almost none of them.