Why Don't we Drink Water from the Ocean?

We know we can't drink salt water from the sea. But why don't we desalinate it?¹

According to the article, 1m^3 of desalinated water costs between 1$ and 2$ , while fresh water from a well/river costs as little as 0.1$ . However, newer dams make the price go up to .6$ which starts competing with desalination. Plus, access to fresh water is limited and subject to droughts, while salt water is available in any coastal area.

Main costs for desalinating is energy, plus residue removal. The salt left behind can't be simply released to the ocean since it would increase the concentration locally, being a risk for life. One method for desalinating is by evaporating water, which demands energy. Can't solar energy (i.e. direct sunlight) be used? I think I remember a paper by N. Halas on the use of gold nanoparticles to absorb visible light, transduce it to heat, etc.

My question: How much fresh water does each human need? Especially if we factor the amount of water needed for growing food.