Evaporative cooling (like a "swamp cooler" for residential homes) is how most data centers in the US are cooled. The water is primarily consumed by evaporation. When you continually evaporate water from a system, eventually the remaining water in the system gets concentrated in salts and other minerals and is dumped and replaced with fresh water.

Much of the day/season, evaporative cooling is not needed and data centers can pull in outside air. Ultimately you state the main reason in your comment: using outside air + evaporative cooling is cheaper and consumes less power than any other approach.

In a lot of cases, even if the server chips themselves are liquid cooled (for example, in an NVIDIA GB200 rack), then liquid is then air cooled through a cooling distribution unit (basically a giant radiator.

Air cooling doesn’t scale. Try having thousands of computers all in your room.

Well sure but why does it need to be open cycle and actually consume water? That’s the problem part, not internal water cooling.

It absolutely does not have to be open cycle, but that saves some money and externalizes the problem in the form of heating up the ground water.

Adding in an evaporative cooling tower almost doubles the efficiency so it costs almost half as much to cool a data center using cooling towers vs air cooled chillers alone.

While air cooling doesn't scale, air also is not a great heat carrier when you cram that much power to a small space.

Today's supercomputers (AI or not) can't cool themselves off with air. Too much heat in a too confined space. Direct Liquid Cooling is a must.

However, you can use closed-loop liquid cooling (like Europe), but open-loop is cheaper since it skips the "pump the heat out from water to atmosphere" part and "who cares about the water anyway, there's monies to be made".

Putting money above the environment always makes me angry though. It's like burning the walls of your house to stay warm.

That’s what I thought.

Yet look at the prices on e.g. Hetzner and how profitable US cloud is. They can easily afford to do closed loop.

Whenever there’s a real environmental problem the answer is usually “there’s a right way to do it that lacks these issues but it’s slightly more expensive.”