It's funny how useful water is for power generation.
There's heat storage as discussed here.
Or you can store cold water in a reservoir as a giant battery, pumping it up high when you've got excess power, and letting it back down to generate hydroelectricity from it later.
Or you can boil water to make steam that spins a turbine and use it to convert anything that can heat water (coal, oil, nuclear...) to electricity.
> It's funny how useful water is for power generation.
It's gravity that does the generation. Water is convenient because it's weight per unit of volume is very high. Higher than most things we can get our hands on and it's also exceptionally safe.
Since water isn't perfectly clean the main problem you face is corrosion. Which can take a great system and turn it into a nightmare of buried leaks and sudden problems.
As far as our options go it _is_ really convenient.
And maybe it's obvious, but the largest thing that makes water so useful is that on our planet it's usually liquid but has easy to reach boiling and freezing points. Most notably a boiling point that is easily withstood by most metals and trivially reached by most methods of heating. Chemically something like quartz would work just fine, but its heating and boiling point are way too high to be practical. Occasionally we do reach for molten salts like lithium chloride