Q: This time of year I get a flood of questions about water law, especially from students. So hopefully I can shine a light into the murky deep by giving a general overview. Then maybe the ebbs and flows of this liquid subject will make more sense.

A: There is not enough water available for everyone who wants to use it. To secure a water right, the general rule is that there must be a "diversion" from its source plus application of the water for a "beneficial" use. Thereafter, non- use of water for ten years sets up a presumption that the right to use water has been abandoned by the appropriator. That presumption can be overcome by evidence of the reasons for non-use and future expected use.

Under Colorado law, water is allocated by having everyone form a line based upon the chronological order when water was first used, starting with the oldest and ending with the newest. Then going down the line, water is disbursed based upon predetermined amounts until the water runs out. Usually, unless a priority date is on or before the 1890s, (at least in northern Colorado), the likelihood of a dependable supply is remote.

So-called tributary water has been found by the court to be connected, whether it is above ground as in rivers, lakes and puddles, or below ground as in ground water and aquifers. Thus, whether water is tributary or not boils down to what the water court determines. There are several famous incidents where Courts determined water to be tributary or non-tributary, where to everyone else it was physically impossible to justify the legal conclusion.

To envision the concept of tributary, think of a sheet of water that is both above and below ground, where removal of water will eventually affect water available in the rest of the sheet. Thus, pumping water from a well means that to replace the removed water, the surrounding water within the sheet must flow in to fill the void created by pumping.

If a Johnny-come-lately punches a hole in the ground and uses tributary water, he or she is in effect crowding to the front of the water line by taking water from people already in line who use that common sheet of water.

Allocating water access among all users (both surface users and well pumpers) was judicially determined in the 1960s. Each water appropriator was given a place in the allocation line based on when the water right was first utilized. But because wells were normally used later than surface water, well priority dates are normally "junior" to most surface users.

But if a junior well user replaces the water for those ahead of him or her in the line, for example, by buying water for them, then use of the well would be permitted.

The easiest way, or sometimes the court required way, to replace the water taken by pumping a well, would be to join an underground water users association that already has worked out all of the legal details and arranged for the required substitute water to be provided. But for many, the costs of being part of the association means that only a Pyrrhic victory was achieved because the expense might be too high to economically pump the wells.

Non-tributary ground water has been found by the water court to have no connection to surface water. Although some surface water has been found to be unconnected to the sheet of water, this label is usually applied to wells. Thus, non-tributary means that pumping water will not affect any of the users of the sheet of water standing in the water line. Usually this is water that has been trapped below a stone ceiling, preventing that water from being part of the sheet of water.

Or there may be some connection to the surface water, but it may be too small in the water court's judgment to affect the sheet of water, or because of distance and the difficulty of flow through the aquifer, the effect on the sheet of water may be a long time down the road. If the effect of pumping will take 100 years or more to impact the sheet, the water source can be held to be non- tributary. If found to be non-tributary, the water is not affected by the priority system. Thus the attractiveness of having water judicially determined to be non-tributary.

But what if a group of well users start using the non-tributary water? Remember, the priority system does not apply. So ground water basin associations can be formed to allocate the available non-tributary water based on factors such as the acreage overlying the basin.

This is a very fascinating area of the law and not that complicated if a few basic concepts are kept in mind. After having read this column, go to the library or tap into the internet and read a Colorado Supreme Court case. In addition to possibly being a cure for insomnia, maybe the case will make more sense as well as being entertaining.