Most of the driest regions of the world are sitting on billions of litres of water.
You just have to drill deep enough and then have the purifying technology there, and deserts will be turned in to wheat growing land. There's a reason China is going mad on Africa, they'll turn it in to the food bowl of the world in the next 150 years.
https://gracefo.jpl.nasa.gov/resourc...gest-aquifers/
A scenario like that is going to happen long before we all start eating algae snot.