When civilization finds new energy sources, most other technologies level up as well.

Consider one of the biggest problems with desalinization systems: pumping water inland. The actual separation of salt from seawater isn't the most energy intensive part of the process. Desalinization works great for wealthy coastal communities.

But a large nation like the US or China would never be able to fulfill the water demand of its people through desalinization alone because the cost of transporting coastal water inland would be prohibitive.

Enter something like fusion, which is orders of magnitude more efficient on a per pound of fuel basis than fossil fuels and something like distributing water to everyone in the US from the coasts becomes possible.