A Boring Dystopia

The AC systems use adiabatic gas coolers to minimize their footprint and electricity use. An adiabatic gas cooler works very similarly to a standard AC condenser except that there is an aditional piece of media on the air inlet side of the condenser coil which is kept perpetually wet. Basically as air is pulled through that media it evaporates water and cools that air basically down to the local dew point. This means colder air cooling the refrigerant condenser and thus a smaller more electricity efficient condenser.

Adiabatic coolers are especially popular on CO2 based refrigeration systems because of the low critical temp of CO2. Basically once the ambient temp gets above 75-80F a standard gas cooler can no longer liquify CO2 because it just goes supercritical instead which results in a more inefficient refrigeration process. Adiabatic coolers can largely mitigate that issue.

Of course this whole process could be done without using water but it would require more electricity. Basically someone did the math and found out that using water was cheaper than using more electricity so that's what they did. If we want data centers to stop using up all our water then the easiest fix is to just start charging them more for water.