True enough you can run a sewer system with just salt water, but you need special equipment to handle it ~
“San Diego is a DESERT ~ they have a severe fresh water shortage and have to pump it in from hundreds of miles away.”
You appear to have fallen for this specious rhetoric. THERE IS NO SHORTAGE OF WATER, especially for a town located ON the ocean. It is only a shortage of facilities to bring water of suitable quality to the user at a price he is willing to pay.
Israel desalinates sea water and it costs less per gallon than the water I buy from a co-op utility. In both cases, the customer can have all the water the customer wants to buy.
In fact, I can go to a local convenience store and buy as much water that I want from Fiji and from Iceland. It certainly costs more, but again, the folks who sell it are happy to sell me as much as I want.