The lowest water-use dinner I could come up with took 135 gallons of water to deliver two eggs, carrots, potatoes, and a glass of beer. Most dinners are vastly more than that. The biggest takeaway here is that each person in my family of five uses more water in the food we eat than we use together for the house and back yard.
The biggest consumers of water are all proteins: beef, lamb, chickpeas, and lentils. For most meals the protein consumes way more than half of all the water. I was quite surprised to see that chickpeas and lentils, staples of a vegetarian diet, use quite a lot more water than chicken and eggs, which are both about as efficient as one can get, and a full order of magnitude more efficient than lentils, peas, or chickpeas. As I had expected, soy is a water-efficient form of protein.
Arjen Hoekstra, the founder of Water Footprint Network, has spent years researching agricultural water use. One of his messages is that "animal products demand considerably higher amounts of water than do most other food types." (Quote of Mr. Hoekstra from LA Times.) This makes intuitive sense, because animals consume and do not produce protein and carbohydrates. If you ate the stuff that the animal eats instead, that would have to be a more efficient way to get those proteins and calories than by eating the animal.
But people, even vegetarians, don't eat the stuff we feed animals. We feed animals cheap vegetables (like grass and grains and corn mash left over from making ethanol), and eat the expensive ones (like carrots and blueberries) ourselves. The astonishing result is that, overall, meat products deliver way more protein per water used than vegetable products! I came to this conclusion using Mr. Hoekstra's own data.
So here's my analysis. The water usage that the LA Times quotes are for an 8 ounce serving of all the various protein-rich foods. As you might expect, beef has a lot more protein in it than the same amount of lentils. If I correct the serving size to get the same amount of protein in all servings, the ranking comes out like this, from best to worst:
|Food||Serving Size||Protein content||Fat content||Carb content||Water Used|
|Chicken||8 ounces||56 g (224 cal)||29 g (259 cal)||0 g (0 cal)||131 gallons|
|Eggs||16 ounces||56 g (224 cal)||47 g (420 cal)||6 g (22 cal)||193 gallons|
|Soy burger||12 ounces||56 g (224 cal)||19 g (168 cal)||42 g (168 cal)||254 gallons|
|Goat||7 ounces||56 g (224 cal)||19 g (168 cal)||0 g (0 cal)||282 gallons|
|Milk (1%)||60 ounces||56 g (224 cal)||17 g (151 cal)||84 g (336 cal)||359 gallons|
|Pork||9.5 ounces||56 g (224 cal)||15 g (139 cal)||4 g (16 cal)||394 gallons|
|Lamb||5.5 ounces||56 g (224 cal)||48 g (432 cal)||0 g (0 cal)||465 gallons|
|Beef||8 ounces||56 g (224 cal)||33 g (298 cal)||0 g (0 cal)||850 gallons|
|Almonds||9 ounces||56 g (224 cal)||126 g (1134 cal)||56 g (224 cal)||1097 gallons|
|Lentils||22 ounces||56 g (224 cal)||0 g (0 cal)||127 g (509 cal)||1564 gallons|
|Peas||36 ounces||56 g (224 cal)||4 g (38 cal)||147 g (588 cal)||1599 gallons|
|Chickpeas||22 ounces||56 g (224 cal)||19 g (168 cal)||187 g (747 cal)||1670 gallons|
I've added almonds to the table (using Mr. Hoekstra's data again), as they are rich in protein, use a lot of water, and are getting a bad rap in California for their water use right now. I've also listed fat and carb calories. For those of us trying to get to a low-carb, high-protein diet, soy and maybe milk look okay but these other veggie options are not great.
Farmers, of course, don't directly care how much protein their products have, but rather how much profit can be made from them. I wasn't able to get profit numbers, but some quick Googling came up with the following prices. If a farmer and his inputs are constrained primarily by water, then poultry farming looks like a good way to go, and once again vegetarian staples appear to be a terrible choice.
|Food||Water Used||Farm Price||Price per gallon|
|Eggs||1566 m3/tonne||$1.90/pound||1.013 cents/gallon|
|Goat||5521 m3/tonne||$5.25/pound||0.794 cents/gallon|
|Pork||5508 m3/tonne||$4.06/pound||0.615 cents/gallon|
|Chicken||2218 m3/tonne||$1.54/pound||0.579 cents/gallon|
|Beef||14191 m3/tonne||$5.65/pound||0.332 cents/gallon|
|Peas||1979 m3/tonne||$0.70/pound||0.295 cents/gallon|
|Lamb||13007 m3/tonne||$4.28/pound||0.275 cents/gallon|
|Milk||796 m3/tonne||$0.21/pound||0.220 cents/gallon|
|Lentils||5874 m3/tonne||$0.90/pound||0.128 cents/gallon|
|Almonds||16095 m3/tonne||$2.00/pound||0.104 cents/gallon|
|Soybeans||2145 m3/tonne||$0.23/pound||0.089 cents/gallon|
|Chickpeas||4177 m3/tonne||$0.29/pound||0.058 cents/gallon|
It's worth mentioning that tap water in California goes for about 0.55 cents/gallon. If farmers paid for water what I pay, most would stop farming. On the other hand, if most residential water users were charged similar rates to farmers, most would stop conserving water. Things are pretty out of whack.
Prices aren't profit, and California farmers aren't all water constrained. In many places they can pump unlimited (or more precisely, unregulated) amounts of groundwater. In particular, there has been a trend in California of dairies converting to almond orchards. The second table above suggests this is exactly backwards if those products have similar profit margins and are water limited. California farmers are making the move because profit margins on dairy are smaller than almonds and they are not limited by water.