Rathdrum Prairie aquifer future water demand Report uri icon



  • Thirty-one municipal water providers deliver groundwater to 107,660 people over and adjoining the Rathdrum Prairie Aquifer (RPA) in northern Idaho. In 2014, the Idaho Legislature appropriated $500,000 to the Idaho Water Resources Board (IWRB) “to conduct joint water need studies in coordination with Northern Idaho communities to ensure water availability for future economic development”. The Idaho Water Resources Research Institute (IWRRI) was contracted to conduct the studies and report to IWRB and RPA municipal providers. The goal of the contract and this report is to provide underlying information necessary to support potential Reasonably Anticipated Future Need (RAFN) water right applications from RPA municipal providers. Idaho Code authorizes municipal water providers to hold RAFN water rights to provide for future growth and economic development. There are four components of an application for a RAFN right: delineation of the future service area, a planning horizon, a future water demand projection, and a water right gap analysis to determine the extent of the RAFN right to be applied for. Approximately 85,000 acre foot (AF) annually is withdrawn from the RPA for municipal, domestic, commercial, industrial, and agricultural use. Of that, 36,400 AF is withdrawn by RPA municipal providers with eleven providers supplying water to 95% of the RP population. Ten providers anticipate either applying for RAFN rights, or identified potential service area overlaps with other providers. After mediated resolution of overlaps and terms of service, a Memorandum of Understanding identifying future RPA municipal water provider service areas was negotiated and signed by all ten municipal providers. Population served by the eleven major RPA municipal providers is projected to increase by 87,671 over the 30-year planning horizon. The area served will increase from 78.9 square miles to 156.9 square miles. Relatively low to medium density (<1-4 units/acre) development of both ACI and rural areas is likely to constitute roughly 80-85% of new residential development. Existing cities and their Areas of City Impacts (ACI), along with urban reserves, will likely see a small amount (up to 5%) of higher intensity, compact development both within the city centers and at nodes along existing arterial and collector corridors within ACIs and in rural portions of the county. The Maximum Daily Demand will increase by 61.53 cfs, and the Peak Hourly Demand will increase by 171.81 cfs. RAFN rights totaling 58.86 cfs are required to meet the 2045 MDD of five RPA municipal providers. The rights are offset by a decrease of 103.74 in MDD required rights among six other RPA municipal providers. RAFN rights totaling 264.69 cfs are required to meet the 2045 PHD of ten RPA municipal providers. The RAFN rights are offset by a decrease of 32.86 cfs in PHD required rights for one RPA municipal provider. Storage may offset some or all of the PHD RAFN needs of four providers with above ground storage capacity depending on individual provider water storage Management Policy. Appendix A: RPA RAFN Service Area Memorandum of Understanding. Appendix B: Rathdrum Prairie Aquifer 2014 Demand Update. Appendix C: RPA RAFN Water Right Gap Analysis. Appendix D: Rathdrum Prairie Water Provider Reports.

publication date

  • January 1, 2014


report identifier

  • 201404