Q: Your last column was on water law, but it only dealt with how to buy surface water. What about underground water?

A: I try not to write on the same subject in successive columns but water law by far elicits the most inquiries, many from college students.

There are two general classes of ground water - tributary and non- tributary, although legally there is another classification. However, for our purposes, I am dealing with it as non-tributary.

So-called tributary ground water has been found by the water court to be connected to surface water. Think of a "sheet of water," both above and below ground, where removal of water will eventually affect water availability in the entire sheet.

As I related in the last column, allocating water access among surface users was determined in the 1960's when each water user was given a place in the user allocation line based upon when his or her water right was first utilized. Thus water is distributed down the line, much like when we were in elementary school and lined up at the water fountain for a drink. Only here, when the water runs out, those left in the line go thirsty.

Now add the element of someone punching a hole in the ground and taking water in such a way as to affect water availability for surface users. That is why in the 1960's, the water court also integrated both surface and ground water users so both find their place in the same line. Thus, if ground water is found to be tributary, then it is assigned its place in line along with everyone else. But because wells were normally first used later than surface water, well priority dates are normally "junior" to most surface users.

Tributary ground water rights can be bought and sold but, like surface water, just because a "permit" indicates that a certain amount of water can be pumped does not mean that the quantity of water can be purchased with certainty. If water has not been pumped, then it can be deemed to be abandoned (use it or lose it).

Water rights in a well can be moved to a new location but the water court can reduce or even eliminate the amount of water available at the new location because it might adversely affect other users in line - both surface and ground water users. In addition, factors such as distance moved, underlying ground structure affecting flow rates, etc. will be considered and usually greatly reduce the mobility of any significant amount of water, especially compared to surface water.

In many parts of Colorado, well users may also be forced to join a well users association if they wish to pump water. In a very superficial sense because many wells are far down the "priority" list, the association buys water to replace the water used by its members that affect other water users around them.

Non-tributary water has been found by the water court to have no connection to surface water. Thus, 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 either the connection may be too small in the water court's judgment 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 affect the "sheet," it can be held to be "non-tributary." Therefore, the water is not affected by the "priority system."

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 upon factors such as the acreage overlying the basin. Application for use or to transfer wells is usually made to the "ground water basin" governing board.

Thus, even the right to use ground water can be bought and sold, but paying attention to details becomes even more critical when buying ground water if you want to end up with what you thought you were buying.