New Mexico State Supreme Court justices are deciding whether a pivotal, decades-old state domestic well law violates the state constitution.

The five justices heard oral arguments Thursday in two cases challenging the state statute. Their final decision has far-reaching consequences.

If the justices find the state law is unconstitutional, the legality of tens of thousands of domestic wells in the state would be questionable.

If the court finds the state law doesn't contradict the constitution, a big question remains, one that the justices seemed to say the state Legislature would have to resolve: How to ensure an increasing number of wells don't impair the water available to people with priority rights.

The debate over how domestic wells affect farmers, tribes and others with the oldest, and most senior, water rights in New Mexico has deepened in the last several years as the number of domestic wells has proliferated and drought has further limited an already scarce resource.

This is the first time the debate has come before the state Supreme Court. It began when a Southern New Mexico farm couple, Horace and Jo Bounds in the Mimbres Valley, sued the New Mexico State Engineer. The couple has senior water rights on an acequia fed by the Mimbres River. They claimed they weren't receiving their full share of water because pumping from new wells nearby was drying up aquifers that bolstered river flows.

In addition, the state engineer had declared the water in the Mimbres basin "fully appropriated." So if all the water was spoken for, the couple argued, how could the state engineer keep issuing permits for new wells?

The 14,000 member New Mexico Farm and Livestock Bureau also filed a complaint saying the domestic well law was unconstitutional and violates due process for people with priority water rights because they don't have to be notified when a new domestic well permit is issued.

A lower court found the domestic well law unconstitutional, but the New Mexico Court of Appeals disagreed. The appeals court ruled that the priority doctrine — which says that the first person to use water beneficially has the highest right to it — is a "broad principle" and allowing new domestic wells in fully appropriated basins is not contrary to existing water rights law.

Horace and Jo Bounds and the Farm and Livestock Bureau appealed to the Supreme Court, calling the ruling "a dangerous precedent if allowed to stand."

The Office of the State Engineer recognizes the impacts water wells have on aquifers and surface waters. Current State Engineer John D'Antonio has limited the amount of water that can be pumped in some areas, such as the Pojoaque Valley, restricted the ways the water can be used and implemented new rules for sharing water in drought years. Those rules also were challenged by Tri-State Electric among others, and that case will go to the state Supreme Court in November.

Domestic wells enjoy an exemption all other kinds of wells and water uses don't have, the Bounds' attorney Beverly J. Singleman told the justices on Thursday. A developer with 100 acres who wanted to put in a community water well, for example, would have to apply for a permit, send out a public notice, and neighbors could protest, she said. If the developer instead subdivided into dozens of lots and each property owner applied for an individual well, they could get a permit without a hearing or notifying neighbors.

When pumping from those wells impairs a senior water right, that is contrary to the New Mexico Constitution, Singleman argued. The constitution specifically protects priority water rights above others.

Domestic wells weren't a problem when New Mexico was a rural state with few people and few domestic wells. But as wells proliferated, the impacts became more pronounced, especially during drought. "Domestic wells should not have a free pass," Singleton said.

The complainants say wording in the domestic well law is a big part of the problem. State law says the state engineer "shall" issue a domestic well permit, leaving him little choice. Change the word to "may," and the state engineer would have the ability to outright deny a permit if it could affect other water rights.

"I don't believe it needs to be changed," DL Sanders, lead counsel for the Office of the State Engineer, told the justices. "I believe the [state] law is constitutional on its face."

But if it is to be changed, he said, that's the prerogative of the Legislature.

Contact Staci Matlock at 986-3055 or smatlock@sfnewmexican.com.