coastal areas are characterized by less rainfall and can take advantage of sea water,
inland areas can take advantage of rainwater, storing it and distributing it after the purification process
I know it's a little 'out of what is required, but I think that the problem must be resolved in a comprehensive way.
There are many ways to save water, but the truth is that sooner or later it will end.
Well, we can use what we have in nature: the salt water!
The oceans occupy 71% of the earth's surface and only in Italy there are lots of plants for the extraction of salt using the method of evaporation basins.
We just need to find a method to collect the evaporated water and conveying it to our use.