The water supply for the City of Etna is a diversion from Etna Creek about 2 miles upstream of the City. The watershed upstream of the diversion is primarily undeveloped, resulting in generally high quality water most of the time. The diversion is at an elevation that allows gravity flow to the City, through the water treatment facilities and into the City's reservoirs. The reservoirs are located on the hillside above the town, providing gravity flow to the City distribution system and customers. The entirely gravity system is reliable and economical to operate.

Current water supply requirements were estimated to average about 65,000 gpd (gallons per day) and peak at 150,000 gpd. The required water supply is projected to increase to an average of79,000 gpd and peak of 183,000 gpd by the year 2024, the end of the 20 year planning period selected for this study. Those values include a I 0% allowance for losses in the distribution system and a 25% loss to filter backwashing at the treatment plant.

The City has a water right allowing diversion of 2.40 cfs (cubic feet per second) or 1,550,00 gpd, well in excess of the projected demands. The minimum flow available for diversion from Etna Creek during late summer, however, is estimated to average only 0.38 cfs or 243,000 gpd. It is estimated that the flow will be less than the year 2024 maximum day demand once every 2 or 3 years and below the year 2024 average day demand once every 25 years, based on a 7 day minimum flow. Those estimates are based on considerable extrapolation of the limited available data, but they are consistent with reported experience. Further data collection and study is recommended to better define the minimum available flow from Etna Creek.