1. They don't HAVE to use water. Air cooling, closed loop cooling, waste-water cooling, and so on, are options. Easy to regulate. Evaporative cooling is more energy efficient though, but a complete non-issue in places with abundant water and a non-option elsewhere.

2. Datacenters have been shown to reduce utility prices. They provide suppliers with previsible long term demand which allows for cost-effective network and production planning.