Water can be stored almost losslessly, with cheap fixed costs (e.g. the many cisterns in a household, e.g. the iconic watertank that appears in US movies). Transporting water long distances usually has large fixed costs, and has massive marginal costs if it has to go uphill.

Electricity is expensive to store, both marginal costs (losses) and fixed costs (plant). Pumping water into hydro-electric lakes is a reasonable solution at present but: 1. pumping has significant marginal losses, 2. usually lakes can't be placed near significant urban loads (desireble to reduce network failure risk, and optimise network loading), 3. hydro-electric lakes are often hard engineering (earthquake risks, difficult to get good potential energy storage if flat land), or politically difficult (consent, water rights), etc.

We need to invent better systems that can profitably sell peak load and buy off-peak load (or buy constant load). Especially for periods of a day or even longer. That would also solve a lot of issues with eco-friendly power (solar, wind). Especially that can absorb huge amounts of load (e.g. overnight). Especially that can absorb and release load within sub-minute periods. Big engineering :-)