Yes, that's true--assuming that all thermal power plants are built on coastlines and cooled with seawater, and that the environmental effects of local heating of the water are acceptable. However, current plants aren't built by the sea, they're built near the consumers, so when you get a drought then the power supply drops off. This happened in 2006, for example.

The point is that the siting of power plants has a big effect on the distribution network...