[Johnny Electriglide]

The problem with desalination plants is initial cost and maintenance. Paid for by increased water bills and taxes, in a society headed toward economic breakdown from overpopulation, greed, and stupidity. My solar powered house uses about 1/3 the electric for water pumping from my well and our family of three uses only 100 gallons per day versus the average of 800 gallons per day or more in the USA. There is no recycling except for septic treatment and return to the groundwater at depth after seeping down. I have designed water recycling systems like in "Earthship 3" that would support a family of three (population goes down, demand goes down) in a situation of 12-15"annual rainfall collected from 1500 sq. ft. of roof space, and two plumbing systems. The black water would be from grease of dishwashing, small compost toilet outflow, and a "Y" valve from the clothes washer(and greywater overflow/cleanout). The rest of the water would be collected in a low tank with sand filter, for grey water gravity planter output and toilet tank valve pump to upper water tank (each 2500 gallons). The upper tank water is drawn by pressure pump through several filters(and UV) to a pressure tank, for theoretically using the same water over and over when you take a shower.
It is unfortunate that most of humanity breeds until the water pollution, depletion of soil and good water, and pollution of the air to the point of unstoppable climate change beyond adaptation and livability. Along with mercury pollution, persistent insecticides, and other pollutants along with fished out oceans---they take those that could live sustainably with them.
Even Earthship villages where they grow their own food, recycle everything, and have a small manufacturing capability for PV panel and battery maintenance/re-manufacture, and enough breeding intelligent couples to prevent genetic erosion---will get wiped out by the climate change, and global; mercury pollution, or attacks of cannibal gangs that out-gun them. The rich can live in supplied bunkers for a hundred years, but it will take the planet many thousands of years to support human life. Economic breakdown is happening and has been happening as a result of overpopulation. If you can't see it now or what is to come, you better do some more research.
Even the mentioned "euthanasia" is beyond logistical reality to lower population in time to prevent a mass cascading die-off 2040-60 (preceded by 20 years of economic depression 4 times worse than the 1930s from US extreme debt and trade imbalance along with lowering to third world status by immigration), and with the climate catastrophe, a truly ELE event(89% species loss), off the 26 million year cycle of probability(Nemesis), by 2100. Even a massive effort will run out of money fast, and I don't think the momentum can be stopped for running out of water, food, energy, and a benevolent climate. Overpopulation trumps them all, and running out of water, oil, and climate change to malevolent are just coup de graces. Too little, too late. The horror.....