Why are no cadidates talking about our diminishing water supply?

The Southern, Western, and South-western United States has been in a drought for years. Our potable water is diminishing to a degree that we have to ration it. Water is one of the most important resources in the world and one of the resources most taken for granted and ignored as an area of concern. The next president will likely be confronted with the issue of water and yet we hear nothing from any of the candidates about something that will affect a large part of the US. I am sure that a problem affecting so many states will have to be addressed on a Federal level and will likely result in Federal De-salting plants being built on the ocean. Why is no one talking about it?