Desalination is pricy for agriculture because it's a long distance to transport the water. Because of recent technological advances, they are completely reasonable for the coastal cities though. The only reason they don't get built, is to justify the huge capital expenditure, they need 25 year guaranteed contracts, and even though the cost isn't that much ($500/acre foot, $0.45/m^3 or 1000 liters), it's still more than what water costs when it rains.
So, what tends to happen in areas with variable rain, is that when a drought hits, they get constructed, and then it starts raining, there is no reason to use the $500/acre foot water from the Desalination plant, instead of the $10-$125/acre foot [1] from rain. The only places that it is economical to build them is where we are guaranteed that they will be required.
If we could be certain the drought would continue, then yes, we would have desalination plants being built all along the coast (as they are in Singapore, Dubai, etc...). Alternatively, we could just bite the bullet and say we need this type of reliability of water supply and just build them. At that point, we could end all the nonsense about "conservation" in residential areas when there is an agricultural water supply issue. None of the conservation that people are doing in residential areas is going to make a spit of difference to the California water shortage situation - it's purely political posturing.
[1] http://www.ppic.org/content/pubs/report/r_1112ehr.pdf pg 24, footnote. ".... In 2005, under a similar deal, MWDSC did not exercise the options to purchase nearly 130,000 af because there was ample rain, and growers again received just the installment ($10 per af, versus a final purchase price for the water of $125 per af)"
So, what tends to happen in areas with variable rain, is that when a drought hits, they get constructed, and then it starts raining, there is no reason to use the $500/acre foot water from the Desalination plant, instead of the $10-$125/acre foot [1] from rain. The only places that it is economical to build them is where we are guaranteed that they will be required.
If we could be certain the drought would continue, then yes, we would have desalination plants being built all along the coast (as they are in Singapore, Dubai, etc...). Alternatively, we could just bite the bullet and say we need this type of reliability of water supply and just build them. At that point, we could end all the nonsense about "conservation" in residential areas when there is an agricultural water supply issue. None of the conservation that people are doing in residential areas is going to make a spit of difference to the California water shortage situation - it's purely political posturing.
[1] http://www.ppic.org/content/pubs/report/r_1112ehr.pdf pg 24, footnote. ".... In 2005, under a similar deal, MWDSC did not exercise the options to purchase nearly 130,000 af because there was ample rain, and growers again received just the installment ($10 per af, versus a final purchase price for the water of $125 per af)"