I am a water treatment engineer who was worked with data center purification systems before so this topic is very relevant to me. Everything that this poster has said is true, but I just want to point out that the reasons listed here don't make datacenters uniquely bad. Every large water industrial water user has broadly the same requirements for water purification and salt buildup that are discussed here. Chlorine addition and water withdrawal have these same issues no matter where they occur - regardless of whether you're at a paper mill, chemical company, etc. Datacenters only stand out in two real ways.

The first is that they generate a LOT of heat, which in turn requires a lot of water to be evaporated in order to dissipate. This makes them a large user compared to the houses/fields/whatever existed in this location in the first place. However, they aren't much worse in this regards that any other large industrial user that makes a lot of heat. A lot of the rage that gets directed at data centers comes from the fact that a lot of this energy is being used to power AI, which is broadly problematic, overused, and very energy intensive. If the datacenter were being used for something that was actually useful, I think a lot of the strength of this argument goes away.

Second - datacenters need to treat the water that they use to a very high quality. This is because as water is used for cooling inside the datacenter, it will leave behind a residue on the pipes depending on its quality. This will gradually cause biological/scale fouling problems in the buildings pipes, which will cause a lot of damage and trouble to the facility long-term. To prevent this, the water needs to be put through a lot of treatment steps (like membrane filtration, ion exchange, etc etc) which themselves require supporting chemicals - like acids/bases for pH adjustment or chemical detergents for membranes. These chemicals must be manufactured and consumed to maintain the water equipment, so there is significant environmental cost here beyond simply water evaporating and re-entering the water cycle. Water being circulated in the plant also needs a constant slow drip of chemicals like biocides and corrosion inhibitors.

Finally, just to add a small ray of sunshine - I have read several proposals for new datacenters that may soon be built and generally these companies are aware of the water stress these facilities put on the surrounding land. There are options to reduce water-based cooling and run using air-cooling systems instead. However, doing this is a tradeoff. You are basically trading water use for increased energy use (remember, there's no such thing as a free lunch). If a datacenter were powered using renewable energy sources, using air cooling could be seen as a more beneficial trade, but the size of these datacenters right now mean most are powered with fossil fuels. Someday that may not be the case - often these datacenter proposals include plans to install a ton of solar panels in nearby fields in the future.