Desal can potentially alleviate drought in urban environments -- at a steep energy and environmental cost -- but is simply not in the running for producing food at a large scale. For example, ag in California alone consumes ~30 million acre-feet (MAF) a year [1]. The total installed desal capacity worldwide is around 35 MAF/yr [2].

[1] http://www.ppic.org/main/publication_show.asp?i=1108 [2] https://www.researchgate.net/figure/272756219_fig2_Figure-2-...

Desalination seems perfectly capable of creating enough fresh water for agriculture. Desal requires plenty of electricity but with a big investment into new nuclear power plants these demands could be easily met. Switching to irrigation with desal water will come at a cost but I don't think it will be dramatic in the developed world.

Nuclear power has been ideologically poisoned, partly for good reasons, partly for bad (I'm not taking sides here). Whatever the reasons, the effect is that most politicos won't risk a voter stampede to the guy who didn't support reactor building, and as a result, not just in the US, nuclear energy is on its deathbed.

There's some irony in this, because one consequence is that a country's oldest (and hence least safe) reactors will be kept online for longer than planned.

Happily, desal can be powered by solar as well, and in fact this is one application that's OK to run just in the daytime, as the daytime's fresh water can be buffered overnight.

Is there ever talk about passive solutions? I.e. Just pumping vast quantities of sea water over open channels and letting evaporation take its course. It sounds infeasible but maybe there's a way to make an evaporative option viable.

Desalinization is a poor solution for irrigation.

In Israel, desal water is not used (read: wasted) on irrigation. That does not make any economic sense.

We use purified wastewater (output of sewer systems) for that. About 85% of wastewater is reused.

This is a good point, and an important one to note. Desal is cool and all, but in pretty much every scenario, other than one where electricity is clean and cheap, water recycling is way cheaper and much more environmentally friendly.

Well, that's because desalination is not nearly as good a solution as computer programmers think it is.

Not picking on you specifically, but I wish that the default hacker mindset, when it comes across a complicated subject that it thinks it has an easy answer for, would be, "what is it about this problem that I don't understand?"

Let's do a quick overview of what desalination would mean for one of the state's central valley agricultural counties. I picked San Joaquin county, because it's a large producer, but not the largest, and because all of the other problems it would have with desalination -- rate of consumption and the challenge of getting fresh water into the county -- put it roughly in the middle of the set. There are counties that produce more agriculture, and there are counties that would be harder to feed water to. We'll just go with San Joaquin for now.

San Joaquin county produces almonds, apples, apricots, blueberries, cherries, grapes, olives, peaches, pears, walnuts, "biomass", beans, corn, hay, rice, safflower, wheat, asparagus, cucumbers, melons, onions, peppers, potatoes, pumpkins, and tomatoes. [1]

California is large and mountainous. To get water into San Joaquin county, you have to pump it 1300 feet uphill, twice (!), over a distance of nearly 50 miles, to get over the coastal range that lies between San Joaquin county and the San Mateo bay. I made a map with an elevation profile for you [2]. And that's taking a short, as-the-bird-flies route, and putting the desal plant into the bay, which I'm sure a few people would have something to say about.

San Joaquin county uses somewhere in the neighborhood of 1500 million gallons per day of water. [3] Firm official numbers are hard to come by, because the nature of agricultural water consumption makes it difficult to measure and also because it's a political hot potato, but this appears to be a number that's somewhere within the range of plausible.

The billion-dollar, ultra-modern, newly-constructed Carlsbad desalination plant can produce around 50 million gallons per day of fresh water (and an equal amount of briney waste water) [4]. It would cost 10 billion dollars to reduce San Joaquin county's agricultural water draw by just 30% through desalination, and that doesn't include any of the expense or logistical challenges of actually getting the water into that county or dealing with the massive ecological problem the waste would create.

And that's just one county.

In one state.

That's why the people that are in charge of the state's water issues -- the most complex such in the world [5] -- don't take desal as a serious solution to the state's water problems.

I have no idea how you'd apply desal to a situation like Kansas.

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[1]: https://www.sjgov.org/WorkArea/DownloadAsset.aspx?id=25373 [pdf]

[2]: http://i.imgur.com/tD4hMYu.jpg

[3]: http://webcache.googleusercontent.com/search?q=cache:_uwTsIh... [pdf; original doesn't load]

[4]: https://en.wikipedia.org/wiki/Carlsbad_desalination_plant

[5]: https://en.wikipedia.org/wiki/Water_in_California