> And how do they pollute water sources?

In the case of one amazon data center, they were pulling in water that already had nitrates in it due to agricultural run off, but it wasn't enough nitrates to cause a problem for anyone until the data center came. It pulled in a massive amount of water, a lot of which was evaporated and that left behind water with very high concentrations of nitrates.

Normally, the nitrates would be filtered naturally and would mostly remain in the top layers of soil. Amazon pumped out 10s of millions of gallons of the vastly more contaminated water. It was so much water that it was forced much deeper into the ground. It was pushed deep enough to reach the aquifer which contaminated the water source for an entire community of 45,000 people.

Suddenly the water coming out of people's taps was polluted at 10x the federal level for safe drinking water. People got sick. Cancer rates spiked. Babies died. Amazon was forced to settle and pay out 20 million for water treatment and to dig new deeper wells for the community.

> I'm willing to bet that a data center creates a fraction of the pollution of a similarly sized industrial facility such as a chemical plant, refinery, smelter, or steel mill.

This is whataboutism. The existence of other bad things, or even worse things, doesn't make data centers good. They are a problem for the environment regardless of whatever else is also a problem and that's something that needs to be considered every time someone wants to build one. The companies who build and operate data centers should be held 100% accountable for the harm they cause.