Rathdrum Prairie aquifer future water demand: Report to the Idaho Water Resources Board providing information for evaluation of Rathdrum Prairie Aquifer Reasonably Anticipated Future Need municipal provider water right applications.

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 Approximately 85,000 acre foot (AF) annually is withdrawn from the RPA for municipal, domestic, commercial, industrial, and agricultural use. Of that, 36,400 AF is withdrawn by RPA municipal providers with eleven providers supplying water to 95% of the RP population.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 (