That also increases capital costs, putting us back to square 1. Also, have a look at the energy requirements of desal plants. "a few batteries" is pretty gargantuan hand waving
Or you can build reservoirs for freshwater
Very much. Or pump it into aquifers.
Maybe the storage could be part of the energy solution, by pumping to an uphill resovior when power is cheap, and sending it through to downhill resoviors via a hydroplant during the peak hours.
I don't think there are very many places that pumped hydro can be built, where it hasn't been built. You also need quite the significant height difference for it to be meaningfull.
That helps with storage on the output side. But what about the issues/capital costs/resource/labour usage of building huge capacity plant that only gets used 15% of the day?
I don't understand the question. Why can we only pump into aquifers 15% of the day? The point of having massive storage is that you can build a smaller plan and run it all day.
But anyway, arguments about cost of making drinking water are moot. We need it, so eventually all options will be explored as needs increase.