Anything that is a plant and green utilizes water. This water use is driven by the process of gas exchange/transpiration which is required for photosynthesis. Environmental conditions (hot and dry will use more than cool and humid), the percent of the ground covered by the plant (higher percent, more water use, but more yield), and the stage of the plant (large leaves use more than little leaves) impact the amount of water required per acre/plant.

Recently, there has been a lot of press about various cropping systems within California. Many are suggesting that farming in California uses too much water to produce food in a “desert.” This simply isn’t true – California produces a lot of food with a higher water use efficiency than in other parts of the world. This efficiency is due to the use of efficient irrigation systems, good water, soil, and nutrient management, and the ability to deliver water in a timely manner (e.g. plants do not wilt prior to irrigation). 

In a study conducted by the United Nations Food and Agricultural Organization found that it takes an estimated 1 liter of water to produce one Calorie of food. This is equivalent to 0.26 gallons of water/ Calorie. To illustrate the efficiency of California Ag, we can look at a crop that recently has been “under fire:” Almonds. If we assume that it takes 1 gallon of water to produce one kernel, which is equivalent to 28 gallons per ounce, and assume 127 Calories/ounce, this equals 0.22 gallons/Calorie, which is 18% more efficient than the world average. This also does not take into account that hulls – which are fed to dairy cattle as a substitute for alfalfa or corn.

If people want to discuss the efficiency of converting water into food, consideration should be given to the amount of calories and protein that can be produced by that plant. We have to eat to survive, and growing plants require water. Below is a list of foods with a break down of calories and protein produced per gallon of water. Information was sourced from WaterFootPrint.org and Wikipedia. Some plant products have secondary uses as cattle feed, which increases caloric efficiency. What is amazing, at least to me, is how much water it takes to produce protein produced by animals (1 tropic level above plants). Perhaps the best thing to do during a drought is to give up that steak (Now that is a bit depressing…).

 

Item Serving (oz) Calories Protein (g) Gal of Water to Produce Gal of Water/Cal Gal of water/g protein Animal Feed Produced
Lettuce 3.5 55 0.8 2.88 0.05 3.60
Potato 3.5 77 2 7.60 0.10 3.80
Soybean 3.5 446 36.5 56.23 0.13 1.54
Cucumber 3.5 65 0.5 9.18 0.14 18.35
Wheat 3.5 327 12.6 47.90 0.15 3.80
Dates 3.5 282 2.5 59.77 0.21 23.91
Almond 3.5 455 18 98.74 0.22 5.49 Yes
Corn 3.5 86 3.2 19.92 0.23 6.23 Yes
Banana 3.5 89 1 20.97 0.24 20.97
Cabbage 3.5 25 1 7.34 0.29 7.34
Orange 3.5 47 1 13.98 0.30 13.98
Peach 3.5 39 1 11.80 0.30 11.80 Yes
Tomato 3.5 16 1 5.24 0.33 5.24
Chicken 3.5 214 23 113.51 0.53 4.94
Olives 3.5 146 1 79.17 0.54 79.17 Yes
Rice 3.5 80 7 43.78 0.55 6.25
Eggs 3.5 155 12.6 86.51 0.56 6.87
Pork 3.5 242 27 157.03 0.65 5.82
Beef 3.5 249 25.5 403.72 1.62 15.77

 

Gallons of water to produce adapted from Waterfootprint.org, and nutritional information sources from Wikipedia.org.