>What's preventing them getting cool water from a lake and draining to it again to cool down?

Some do, but most don't since the requirements for using cooling water are relatively strict due to the pipes, equipment, and heat exchangers the water flows through. The water used needs to be free of any biological contaminants (such as bacteria and algae), maintain proper pH levels, and are often then treated with other chemicals such as biocides.

Lake water certainly can be treated to the level needed and used, it's just often cheaper to buy domestic water from the local utility than to construct and operate a small scale water treatment system along side the industrial process.

> Where is water going after usage since there is literally zero water consumption?

Most of the water is "consumed" via open loop evaporative cooling systems, so the water is never really "used" as in destroyed or anything. The majority of it is evaporated and returns to the land as rain and the rest is returned via sanitary drains, to city sewer systems.

It cools down the machines by evaporating, and is then released into the atmosphere. That also means the water needs to be clean, pretty much drinking water, because otherwise the evaporation would deposit minerals and stuff.

Turning water into steam uses much more energy than heating water, which means it's a much more effective means of cooling.

What you describe is the type of cooling used in certain power plants. That heats the lake though, which has its own environmental effects https://en.wikipedia.org/wiki/Thermal_pollution

Some smaller data centers have a cool solution where they deposit extra heat into the municipal hot water grid, which is pretty neat https://www.techradar.com/pro/finally-some-good-usage-this-d...

Evaporation losses will move the water to a different locality. DC's not only cool servers, but control humidity by adding or removing water to the air.

Warm water fed back into the ecosystem will (relatively) quickly cause unwanted changes to the lake's biosphere.

Unless it's properly filtered, returned water will be contaminated by material in the cooling system.

It puts local demand on the water system competing with human need.

> Unless it's properly filtered, returned water will be contaminated by material in the cooling system.

Any wastewater is regulated and typically doesn't need to be "filtered." For regular operations, water is treated but the evaporative process leaves most treatment chemicals behind.

Some data centers use evaporative cooling instead of a closed loop.

If you don’t cool the water down before putting it back, you’re just creating heat pollution.

Now try again with local and short term impacts on the whole ecosystem instead of saying "Ackchyually water never leave the atmosphere so it's unlimited"