Waste heat recovery is a thing, and the economics usually work out in your favor if the feed material is really hot. If it’s only mildly warm, you’ll need a lot of machinery to concentrate the heat and raise the temperature to a useful level. At some point, the investment just gets absurd and the idea gets scrapped.

Using heat as heat makes the most sense, since there are fewer steps where you lose some of the heat. Theoretically, you could boil water with server heat, but the massive investment is probably the reason why that isn’t happening everywhere. Running reverse osmosis probably won’t work, because you need electricity for the pumps, and converting heat into electricity comes with significant losses.