This is insane. Strangers happen upon your property asking for water and the law mandates that you oblige? This translates to a number of things, one being that I would likely have to open my door and be accessible to them. They can kiss my boot heels and pound sand with tabasco on it.
That law goes way back to frontier days. You can go for days without food, but the desert can kill you in a matter of hours without water. If I remember right, the language of that law assumes that the other party is practically on the point of death. The law does not require that you endanger yourself, nor does it prevent you from calling the local Border Patrol or Sheriff.