I have been blogging about this for 3 years: Google 'vacuum desalination'. It uses high school physics to turn river and sea water into drinkable fresh water. We could have the paradoxical event, of the water main refilling the reservoir during the summer.
We have a chain of solar driven vacuum pumps of the river or sea boundary. These raise the water up 1m – and it boils. We then pump the water vapour to the nearest water treatment site – and add it to the treated water.
The processing site has level sensors, so reverses the flow – so pumping the water back towards the reservoir. So we charge the water main up with desalinated, pure water: no salts or contaminants. http://jonsthings.blogspot.co.uk/2017/05/ending-drought.html
The UK is surrounded by sea, so coastal villages produce 300% of the water they use – so pump 200% back in shore. So for the price of a 1W solar vacuum pump, and 5W of water vapour pumps, we have endless fresh water. Which can never run out.
So reservoir water will actually be the dearest water in the water main. The vacuum desalinated water is 2% the cost of mains water.
So water can site the pumps on their land, and sell the water to the water grid. And get an annual income of 80.000. So no drought in the UK - ever.