There would be enough water if the state governments were NOT corrupt pieces of ****.
Eeek, I must preview even if I think I got it right.
ironically even though it is expensive:
https://mywaterearth.com/the-cost-of-desalination/
The cost is about double that of water obtained from building a new reservoir or recycling wastewater, according to a 2013 study from the state Department of Water Resources.in 2015. This plant will provide about 7 % of the water needed for San Diego and its surrounding area. They have more than 16 more plants in the works to provide water for California. That should answer your question of whether Desalinization is the solution for coastal regions with growing populations.
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I think over the next few years as more and more fresh water is required the cost of desalt plants will drop.