“Why couldn’t coastal areas use salt water for toilets....”
Several problems with this...
First the infrastructure...it would require 2 sets of water mains for delivery...cost prohibitive!
Second the waste water...there would soon be a high salt content at the waste water treatment facility and would stop the recycling of water. Or it would poison fresh water streams and bodies of water with salt.
And just a comment on toilets...the toilets required today have small tanks that deliver less water for flushing stuff...and many times it is necessary to flush a 2nd time to get rid of the waste. This results in a higher water usage with this small tank toilets.
I like the Thorium + Desalinization idea better than my own, but I was just throwing up ideas here to see what stick on the wall...