The state groundwater laws allow for certain uses of water from a private well without obtaining a permit or certificate. These wells are commonly called "exempt wells". These uses include domestic or industrial (agriculture) at up to 5,000 gallons per day, up to 1/2 acre in area for a lawn or non-commercial garden, and an unlimited amount for stock watering purposes.
However, it is important to understand that there is not an absolute right to always use a 5,000 gpd domestic exemption. Under a number of circumstances, uses of water under the exemption may be curtailed or not allowed. The 2005 Attorney General Opinion on stock watering specifically addresses the question whether Ecology may use other legal authorities to limit or restrict use of exemption. The following material is quoted directly from the opinion:
Although Ecology lacks authority to categorically limit the amount of water that may be withdrawn for stock-watering purposes without a permit, other statutes that authorize Ecology to regulate the use of water may affect withdrawals for stock-watering, just as they may affect other exempt withdrawals and withdrawals requiring a permit. For example, in Postema v. Pollution Control Hearings Bd., 142 Wn.2d 68, 94-95, 11 P.3d 726 (2000), the Supreme Court held that where Ecology has closed water bodies and ground water in hydraulic continuity with such bodies to new withdrawals, it may prohibit new withdrawals that “will have any effect on the flow or level of the surface water.” Such a new withdrawal might be a new withdrawal for stock-watering or it might be a new withdrawal for some other purpose. As a second example, consistent with principles of prior appropriation, Ecology has authority under RCW 90.44.130 “to limit withdrawals by appropriators of ground water so as to enforce the maintenance of a safe sustaining yield from the ground water body.” See also RCW 18.104.040(4)(g), authorizing Ecology to limit well construction in areas “requiring intensive control of withdrawals in the interests of sound management of the ground water resource.” Depending on the specific facts and circumstances, then, these statutes could affect withdrawals for stock-watering purposes, just as they could affect withdrawals for other purposes.
AG0 2005, No. 17, pp. 7-8.
In the case of the proposed Walla Walla instream flow rule and other instream flow rules that have been established, Ecology has limited or closed uses of the exemption under these authorities to protect existing water rights and instream flow rights.
Further, an exempt use is a water right with a priority date like other water rights. If use an exempt right would impair any senior water right (which includes instream flow rights), such use would be subject to regulation. The actual water right associated with the well is determined by the amount of water put to a beneficial use. So in the future if a judicial review of all water rights (an adjudication) were to occur, and water availability was limited, the private well user would probably have a right to the amount beneficially used and a seniority date tied to the first use of the water. A similar analysis might take place by a judge if a neighbor claimed to have a senior water right which was being impaired by the private well.