Idaho Water Use in 2015: Irrigation, Aquaculture and Homes

By Erin M. Murray, U.S. Geological Survey. Fact Sheet 2018–3036, July 2018.

Why count water use

Managing water starts with knowing how much people use. Every 5 years, the USGS estimates water use for every county — by source (fresh or saline, groundwater or surface water) and by use: irrigation, thermoelectric power, industry, public supply, self-supplied domestic, livestock, mining and aquaculture. Idaho matters nationally: in 2015 it ranked third in the nation for total water use. The data are in a USGS data release (Murray, 2018).

The totals

Figure 1: Idaho's 2015 withdrawals by source and category, in million gallons per day (Mgal/d). USGS.

• Total: 17,737 Mgal/d of freshwater — 12,384 from surface water (about 70 percent) and 5,353 from groundwater.
• Surface water served mostly crop irrigation, aquaculture and mining; public supply, domestic, industrial, livestock, golf course and power plant uses relied mostly on groundwater.
• The top three — irrigation, aquaculture and public supply/domestic — used 17,534 Mgal/d, more than 99 percent.

Figure 2: withdrawals by county. Use is highest in southern Idaho, where irrigated farming dominates. USGS.

Irrigation: 15,273 Mgal/d

• Water for nearly 3.78 million acres of crops — 17,108,000 acre-feet a year, 86 percent of all withdrawals.
• Mostly from surface water, chiefly the Snake River — yet irrigation was also the biggest use of groundwater (4,882 Mgal/d, 91 percent of it).
• Crops consumed about 58 percent; the other 42 percent returned to the water cycle through canal losses, runoff and seepage.
• Second in the nation, behind only California.

Figure 3: withdrawals by use in each county, with the share of irrigation water consumed by crops. USGS.

Aquaculture: 1,965 Mgal/d

11 percent of withdrawals, 98 percent from surface water. Idaho has consistently ranked first in the nation, thanks to flow-through raceways: the water diverted to fish farms returns to the river with little lost to evaporation.

Homes: the nation's highest per person

• Public supply — water from community systems — was 1.6 percent of withdrawals, 89 percent of it groundwater; 84 percent went to households, the rest to businesses, parks, pools and buildings, system maintenance, and leaks.
• Seventy-six percent of Idahoans get water from a community system; 24 percent supply their own, from a well serving fewer than 20 homes.
• 2015: 234 Mgal/d delivered to homes by public supply, 70 Mgal/d self-supplied.
• Per person: 184 gallons a day — the highest in the nation, 102 above the national average of 82. The dry West means lots of water for lawns and gardens. Only five counties — Bear Lake, Bingham, Bonner, Boundary and Gem — were at or below the national average.
• Idaho is largely rural, with about 1.7 million people in 2015, so some counties use little water in total despite high use per person.

Trends, 1985–2015

Figure 6: withdrawals by source, 1985–2015, and population. USGS.

Idaho's population has grown steadily since 1990, but total withdrawals have held steady or dipped slightly. From 2010 to 2015, more people joined public systems and fewer supplied their own; about 40 percent of the growth was in Ada and Canyon counties. Because irrigation dominates, year-to-year totals rise and fall with weather and irrigation practice.

What's needed next

• Irrigation: better measures of seasonal demand in farm counties.
• Aquaculture: how much water it actually consumes, versus what it returns.
• Cities: more detail in fast-growing areas, why household use is so high, and how much goes to lawns and gardens — especially in Ada and Canyon counties, where growth could push use up or down.
• Finer detail: estimates more often than every 5 years, and below the county level.

Sources

Based on Idaho Water Use, 2015, by Erin M. Murray, USGS Fact Sheet 2018–3036, U.S. Geological Survey, with data from the Idaho Department of Water Resources, USDA, the Bureau of Reclamation, the U.S. Census Bureau and others; a work of the United States government in the public domain. The four figures are taken from the fact sheet's PDF, which the import had left out; the map's neighboring text is blanked. The fact sheet gives public supply and domestic use together as 276 Mgal/d, less than the sum of its parts, 234 and 70.