Cape Town apparently decided to use desalination.

https://resource.capetown.gov.za/documentcentre/Documents/Graphics and educational material/Desalination_Booklet_English.pdf

Permanent desalination is planned because seawater is available all the time, whether it rains or not, so it’s more reliable than any other water source. About 97% of water on Earth is in our oceans. We can make use of this huge resource through the process of desalination, which makes it drinkable and usable for us. Although desalination is the most expensive supply option and there are environmental issues that need to be well-managed (such as the salty ‘brine’ it produces as a waste product), it is an important part of the diversified water supply ‘mix’ going forward.

Says they start construction in 2026 and expect production starting in 2030.