While Cally Carswell's piece might better have been titled "Death by more than a hundred thousand wells," the issue is not the present number of wells but the potential for the future growth of this phenomenon (HCN, 10/26/09).
The exempt or domestic well is increasingly being recognized as the fly in the ointment of prior appropriation. New Mexico's rules for domestic wells hold that "the right to divert water under this permit is subject to curtailment by priority administration as implemented by the state engineer or a court." However, that State Engineer John D'Antonio testified in court that "he would not subject domestic wells to a priority call" despite what the court notes is "a derogation of his duty," speaks to the invincibility of the domestic well, which is arguably a water right like any other. The bottom line is that the states do have the ability to regulate these wells, but generally choose not to owing to the political ramifications of shutting off people's drinking and domestic water to irrigate hay.
Without explicit planning for and management of exurban growth via intelligent land-use planning programs at the state level, such growth will never be constrained by water policy until it is much too late.