Coal and nuclear powerplants make heat, convert some of that to electriciy, and reject the rest. They use water, and lots of it, to reject the heat.
The USGS says that thermoelectric powerplants (nearly all coal and nuclear) use 49% of the water withdrawn in the US. That sounds like a lot, and it is. It's also misleading.
92% of the water used by powerplants is used for once-through cooling. That means they suck water from the river, use it to cool their condensers, then pump it back the river at somewhat higher temperature. There are legal limits to the temperature they can send back out, and as the intake water temperature rises closer to those limits, they have to pump more water, and eventually shut down the powerplant. This has happened, famously, in France during a heat wave, right when everyone wanted to run their air conditioners.
The other 8% of the water used by powerplants is used in recirculating cooling. In these systems water is used to cool the condensers, but then some of that water is evaporated in those familiar hyperbolic cooling towers, which cools the rest, and the water is cycled around. These systems use a lot less water because they only need to make up the water that evaporates. Of that 8%, about 70% is evaporated and 30% returned to the lake or river it came from.
Since 1990, the US has mostly built gas-turbine powerplants. These reject heat in the form of incredibly hot jet exhaust, and don't need water. But they burn natural gas which has caused us to send our plastics industry to China. I don't think many people appreciate how dumb that was.
New nuclear plants in the US will be either on the coastline or evaporatively cooled, because there is no appetite for increasing the amount of once-through freshwater cooling. And I don't think there will be many evaporatively cooled plants at either greenfield or brownfield sites: Greenfield evaporatively cooled plants require new water rights which are very difficult to secure. Brownfield replacements of older coal fired powerplants will be difficult because nuclear plants are much bigger than older coal plants, reject a lot more heat, and so need a lot more water, getting back to the new water rights problem. That leaves new PWR development for areas with a lot of water (US southeast) and coastlines. [Edit: And any new coastline PWR developments are going to face new hurdles as a result of Fukushima.]
Water rights are one reason why I'm so interested in molten salt reactors. MSR cores and turbines run at higher temperatures than those of pressurized water reactor cores, so they can be air cooled without killing their efficiency (and thus jacking up their costs a lot). Air cooling is a good thing because it removes an entire class of regulatory problems, and thus an entire kind of project risk.