That's a tough call. Water's a pretty basic resource but that doesn't make providing it any less artificial. Even on this site, I think we provide conflicting advice on this sort of thing. On the one hand we talk about creating backyard wildlife habitat and providing the resources wildlife needs and on the other we talk about not doing anything that will make wildlife less wild. That's a fine line. Remember, these animals evolved in that environment with its limiting resources. Provide those resources and you take away the limits, which can upset the natural balance. I guess ultimately my advice is to try to make your property mimic the local natural environment as closely as possible and try not to do anything that will cause the animals in it to become habituated to close human presence. I recognize that in a devastated ecosystem such as the San Joaquin Valley, it's hard to know what the natural environment really looked like. Keep in mind also that survival rates of most young animals, not just foxes, aren't particularly high but that most animals produce enough young to overcome that and maintain stable populations. The fox population in your area probably is artificially high as a result of supplemental food (and water?) sources and the elimination of larger predators. Hard years that result in higher fox mortality probably help keep their numbers under control somewhat.