That's fantasy: you can't pump water for long distances and you need to make it fall to get electricity back. Salt water pollute land, corrode turbines and pipes quickly, can't be used anyway, surely can't be used from the sea to the mountains.

Not only: a small lake can store enough for a single home, not more. Pumped storage is far from efficient in energy terms. Consider a thing: we (nearly all nations on the world) have already implemented much of the hydro we can make, simply because it's effective and cheap. We can just do a bit more, but a bit.

BTW the principle is:

- you have a large basin in altitude, with some gates to control the falling flow

- you have a river with a low altitude lake because anyway you do not pump all water back, nor you can't recovery it once used to produce energy and we talk about much water

- you have pipes and turbines and pumps with other pipes

Normally you let a bit of water falling in the pipes making turbines turn producing electricity. When demand low a little bit you just divert part of the falling water out of turbines, eventually pumping back a bit, if the demand fall MUCH you need to consume to keep the network frequency. Normal hydro pump back very little water. With p.v. and eolic who can produce a significant amount of energy just few hours/day you can pump more. So from the low altitude basin/lake you pump back to the higher one. That's is. Depending on the meteo you need to dump more or less water, or you have too little quantity to produce etc.

That simple game means you can't do hydro anywhere on any mountains and grabbing water even far from them.