Where does all the Colorado River water go? A huge amount goes to grow cattle feed, new analysis shows.

In 16 of the 21 years from 2000 to 2020, humans used more Colorado River water than was produced by the spring runoff, according to Richter’s analysis. The overuse drained water from the two major reservoirs on the river, Lake Mead and Lake Powell, which are now only one-third full.

On average, human use combined with evaporation took about 19.3 million acre-feet of water out of the river yearly between 2000 and 2019.

Evaporation sucks up a chunk of the river — and that amount is likely to grow as climate change fuels warmer temperatures and drier air. On average, evaporation from reservoirs, soils and plants takes 30% of available water from the river system.

Water evaporated from the surface of Colorado River reservoirs accounts for 11% of the river’s water loss. Another 19% is consumed through evaporation from soil surfaces and plant leaves in ecosystems along the river and its tributaries.

What are people using the river water for?

After evaporation is accounted for, a quarter of the water diverted for human use is consumed by municipal, commercial and industrial purposes. The remaining three-quarters of the water goes to agriculture.

Ricther and his team analyzed data from a variety of sources to create the estimates in their report. They used data from the Bureau of Reclamation, the Arizona Department of Water Resources, the U.S. Department of Agriculture and previously published studies on the Colorado River.

Agriculture has long been the dominant use of Colorado River water, Richter said.

The basin produces billions of dollars of agricultural products every year, including a majority of the country’s winter vegetables, according to the Arizona Farm Bureau.

What crops are we growing with that water?

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