I've seen people dig ponds and do the "swimming pool" type of thing, where one end is like only a few feet deep and the other end is like really deep, as deep as the machinery can make it.
So it in some way acts as a "water well" where no matter what happens there is water there.
Or the good old wind mill and hand water pump, like in the old western movies, so there is a natural flow of fresh water all the time!
Either way, you are using what mother nature has to offer to make yourselves something that some people could only wish for!