California is experiencing one of its driest years in the past half millennium. It also happens to also be the country’s leading dairy supplier. With profits surpassing $7 billion in 2012, the California dairy industry is far and away the most valuable sector of the state’s enormous agricultural bounty. Unfortunately, as the chart below shows, dairy products use a whole lot of water.


Why is our dairy so thirsty? According to a 2012 study in the journal Ecosystems by Mesfin Mekonnen and Arjen Hoekstra, 98 percent of milk’s water footprint comes from cows’ food.

Now, cattle eat all sorts of things, but a dairy cow’s diet in the United States consists primarily of alfalfa hay, grass hay, corn, and other grains like soy or canola. Alfalfa hay is a superfood of sorts for dairy cows — it’s high in protein, high in energy, and it’s digestible. “When you feed alfalfa, you produce more milk,” says Dan Putnam, a plant scientist at the University of California-Davis. “That’s the bottom line.” In a University of California alfalfa blog (yes, that exists), Putnam and his colleague wrote, “The next time you have pizza (with cheese), milk on your cereal, or ice cream, thank alfalfa.”

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Putnam used a University of Wisconsin study to estimate the amount of milk an acre of alfalfa hay can to produce in a year. If you consider Putnam’s calculations and the California Department of Water Resources’ statistics on the yield of an acre of alfalfa, the water footprint of a gallon of milk looks something like this:


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Given the size of the state’s dairy industry, it may come as no surprise that, as of 2010, alfalfa led the state’s crops in total water consumption and was a close second in total irrigated crop area. Here are some of the other top water users:


The vast majority of alfalfa grown in California is fed to California’s cows, but as the New York Times recently reported, some of the state’s alfalfa hay — Putnam estimates about 10 percent — is shipped abroad, where farmers can reap higher profits.

​Unfortunately, the water footprint of meat products is even bigger than that of dairy. According to another study by Mekonnen and Hoekstra, it takes a total of 425 gallons of water to produce a four-ounce serving of beef in the United States. The same size serving of pork takes 165 gallons of water; for chicken, 66 gallons.

The same New York Times piece suggests that replacing half of the animal products in your diet with plant-based substitutes reduces your food-related water footprint by 30 percent. Going vegetarian reduces it by 60 percent.

This story was produced by Mother Jones as part of the Climate Desk collaboration.