Sure, 70% of the earths surface is water. 97.5% being salt water and 2.5% being fresh water. You can't use sea water to irrigate agriculture. You can't drink sea water from the faucet. Additional money/ cost and work would be need to make the water drinkable. Please consider that many states like California, Nevada, Arizona, Texas, water is a valuable resource. And yes, we are running out of cheap drinkable water. That's why most of the west coast gets most of their water all the way from Colorado.
desalination exists. the key word in is cheap. It's an economic and energy problem, not a water resource problem. They get water from Colorado because its cheaper than desalination. Once it's not, they will get water from the ocean.
also, all water requires money / energy to process before we drink it or use it on crops. It's just a matter of much money / energy you use depending on the source.
