I've heard that just as big as their desalination efforts are their water reuse efforts. All that sewage we work so hard to get rid of? Turns out that's still fresh water. Sort of. It's just got some other stuff in it is all.
http://www.smartpeoplepodcast.com/2015/10/26/episode-214-set...
tldr; water was used as an excuse by the British to limit immigration to Israel, so from the earliest onset of the formation of Israel, Israel has been trying to tackle the problem of water use inefficiency.
http://www.lacsd.org/waterreuse/
I guess in many areas it is less urgent so it doesn't get done.
The Groundwater Replenishment System (GWRS) is the world's largest system for indirect potable reuse. The system takes highly treated wastewater that would have previously been discharged into the Pacific Ocean and purifies it using a three-step advanced treatment process.