posted 15 years ago
In general, western states - and I believe Montana is one - use the prior appropriation doctrine to determine who has the right to use stream water - the people with the oldest rights can satisfy their entire claim, and if the available water is all allotted before the less senior folks can claim any, well that's just the way it is. Many western streams are over-appropriated - there are more existing water rights than there is water, even in a good year.
Also, in most western states, a water right is a right of use. If a senior user is not making good, efficient use of his/her claim, a junior user can contest the amount of a senior right, and get it reduced. The extra water then becomes available to the junior right holders, in order of seniority.
A water right is often not a property right that can be bought and sold like, for instance, a mineral right. Usually, in the west, the water right stays with the land.
A surprising number of western ranchers will readily state that water that reaches the ocean is wasted. Screw the fish and the fishermen, in other words.
This general picture is confused by the existence of water districts/projects, which will have different internal rules, and by instream water rights, which a number of western states now allow for. Typically, the state government or a private entity will gain control of a senior water right, and then that amount of water must stay in the stream. Even if you, the junior water right holder, are watching your pastures turn crisp, you must let that water run by your irrigation gates.
If you live in any of the western states and are buying rural land, you are well-advised to talk to the local water master - and there will be one. The fact that you have property on a permanent stream or on an irrigation canal does not necessarily mean that you can count on using any of that water (although there is such a thing as de minimis use, which means watering the lawn). You *must* understand your situation, or you can get in big trouble. Don't take the realtor's or the seller's word for it, either.
Also, western states have started grappling with the issue of ground water as well. I don't know whether any states have yet started demanding proof of ground water availability before allowing well drilling, but in some areas, folks who already have wells that they depend on are getting pretty worried about how many new wells are being drilled.