They have desalination plants in the middle east. The problem with those is that they are very energy intensive.

I think solar heat desalination plants in very hot climates like that could be more practical. +40C is fairly common in Singapore and the Middle East

There's a large desal plant in Florida too, it supplies part of the water that I drink. You're right in that it's energy intensive, but at least in our part of the world the largest problem was water quality. There's a lot of biomass floating around in sea water and it means having to constantly repair the filters. I believe there was a big issue with an invasive species of mussels as well that do quite a bit of damage.

http://www.tampabaywater.org/facilities/desalination_plant/i...

The pacific is worth mentioning too...Singapore in particular, and Australia increasingly so. A handful of southern US states are getting things ramped up too.

Another problem is the output flow is more saline, which affects sea life.

Can't the salt be safely dumped on land?

It's not salt but brine - water with a high concentration of salt. If put on land it would kill all plant life excepting a few highly salt tolerant species.

The suits in the novel "Dune" do that as well. But there is no ocean or other open bodies of water on the planet in the story.