In Melbourne, Australia, since tap water mostly comes from catchments in national parks, water requires very little treatment (some fluoride and chlorine is added), so it works out cheap: ~$25 AUD per million liters. Desalinated water, by contrast, cost about 24 times more (~$600 AUD per million liters).
I know I would.
Yes, you'll never have to worry about your basic supply of 50 gal/d/person being threatened in a drought, but just think about this for a second: the population of Melbourne is around 5 million people. In the 2020-2021 year, Melbourne Water delivered 439 billion liters (116 billion gallons) of fresh water[1]. That is roughly 318 million gallons of water consumption on an average day. What kind of drought would reduce the available water from 318 million gallons to 25 million gallons per day?
Personal consumption (drinking, showering, household washing) is not the primary driver of water use. In general, it is dominated by agriculture, and to a lesser extent by industry. The economics of these activities would not permit an order of magnitude increase in the cost of fresh water.
Australia uses a estimated ~16T liters of water per year [1] for all uses including personal and agricultural. That is 16M ML * 600 AUD/ML for a total of ~10B AUD.
Australia has a population of ~25M. So that is ~400 AUD/person to completely replace all water usage in Australia. As Australia is a island, I assume they do most of their own agriculture, so for additional 400 AUD on their food bill a year they never need to worry about a drought ever again.
The Australian government appears to have a budget of ~500B/year which is around 25% of GDP [2]. So, for ~2% of the government budget or ~0.5% of GDP the economics are completely managed.
[1] https://www.worldometers.info/water/
[2] https://www.aph.gov.au/About_Parliament/Parliamentary_Depart...
You can see the numbers don't match up; you're using a figure of 16T liters annually, whereas 25 million people * 50 gallons / day-person * 365 days * 3.785 liters/gallon is 1.727T trillion liters annually.
Anyway, I am suspicious of the 600 AUD/ML figure, or else a lot more Gulf states would be food independent.
600 AUD/ML is ~400 USD/ML. The Sorek B plant in Israel is profitably contracted at ~0.40 USD/m^3 [1] which is comparable. That is one of the largest plants with cutting edge technology and one of the cheapest prices I have seen in my research. A quote of 600 AUD/ML for desalinated water right now in Australia seems a tad questionable, but not outside of what is possible. 2-3x that number is almost certainly believable (though they almost certainly do not have bulk scale) and would only increase the costs to 1.5% of GDP.
The cost of simply keeping it turned off is $500,000 a day.
Simply building bigger dam walls would be a far better choice.
Raising the few dam walls that service Sydney is nowhere near the same cost but people are very angry about it ever happening because it would basically remove entire flood zones from the planning maps and encourage development in their areas.
How? I don't understand what that money is being spent on.
from the historical net loss rate approaching the lows one can estimate the required backup desalination flow rate.
For human consumption: this is pretty much true. Desalinization works just fine for people. The biggest issue is where to put the extra salty waste products.
When people talk about the "water crisis" in the US, for example, it's always about big agribusinesses doing farming.
The U.S. has "salt farms" where they evaporate water to produce salt. Sounds like colocating near the desalination plant would make those cheaper to operate.