California’s drought has spawned a flurry of social media articles with titles like “It takes how much water to grow an Almond?” and “Don’t eat meat! Vegan diets use less water”, and graphs of how much water it takes to make a pound of different kinds of food. But for practical purposes, these articles are useless because A) nutrition is not measured in pounds, and B) they are picking on specific foods instead of considering a complete balanced diet.
It’s time to run the numbers!
I researched water footprints of 150 different ingredients from waterfootprint.org, and nutrition information from wolframalpha.com. I also filled in 12 additional essential nutrients from whfoods.com. I even put in the 9 essential amino acids. “Essential” means your body cannot make them, so you have to eat them. All in all I analyzed 43 essential nutrients, plus cholesterol. I put in an option to take a multivitamin pill, with or without vitamin A, since too much vitamin A is associated with reduced bone mineral density. For fun I generated nutrition labels using caloriecount.com.
I ask, what is the minimum total water usage that can produce a healthy diet, according to the FDA’s recommended daily intake of each of these 43 essential nutrients? Well that’s just a linear complementarity math problem, and luckily Excel can solve those! Into the spreadsheet it goes.
Without further ado, here is the minimum water usage diet, assuming vitamin pills and fish use very little water:
Boom, only 845 Litres of water per day! You’d take a multivitamin to make up for the missing nutrients, especially folate, making sure not to add any more vitamin A. Unfortunately I don’t know how much water it takes to make one multivitamin pill, so this might not be fair. More importantly, this diet is totally gross. So let’s remove the vitamin pill:
4g beef liver
25g brussels sprouts
394g green peas
12g poppy seed
317g tomato paste
This diet requires 1560 Litres of water per day. I capped the quantities for spices, otherwise you end up eating lots of ginger and turmeric. It’s slightly less gross than the first diet, but it’s still a lot of food and it’s heavy on starches.
Let’s try making diets that are less gross. I added some minimum requirements for the 4 basic food groups from Harvard’s Healthy Eating Plate. First, allowing the vitamin again:
This balanced diet requires 1389 Litres of water, plus whatever water a vitamin pill uses. It actually sounds edible, thanks to the balancing of the food groups! Now without the vitamin pill:
4g beef liver
283g brussels sprouts
12g palm oil
15g poppy seed
92g string beans
272g tomato paste
Well now we’re up to 1918 Litres of water per day. Such is the price of a balanced diet with food-sourced vitamins. At least it sounds delicious!
Okay now how about a vegetarian diet? Let’s remove all the ingredients that involve eating dead animals that are large enough to see with the naked eye, sticking with the no-vitamin rule:
The vegetarian diet uses 2057 Litres of water per day. Clearly, adding more constraints on your options can only worsen the objective (minimizing water). How about vegan? We’ll remove all ingredients that are stolen from helpless animals, again with no vitamin pills:
That’s 2873 Litres of water per day for a healthy vegan diet. I hope you like cauliflower. Anyway, lowering your water footprint by going vegan is clearly a myth. That’s just simple math: adding more constraints can never improve the objective. To be fair, let’s find the optimal omnivore diet if we require one 4 oz steak per day:
432g brussels sprouts
50g lemon / lime
4g maple syrup
19g palm oil
11g poppy seed
2g soybean oil
359g tomato paste
This steak diet requires 3271 Litres of water per day. It’s more than the vegan diet, but not that much more. I’m going to say, myth busted. Vegetarians win here, actually. I had to cap the molasses to 133g (the same as vegetarians to be fair), otherwise it was over 200g and, well, yuck. How about requiring 4 oz chicken?
275g brussels sprouts
50g lemon / lime
21g palm oil
8g poppy seeds
281g tomato paste
That requires 2134 Litres of water, which is less than vegan and very close to vegetarian. Wow. So chicken actually does save water compared to steak. Okay, all these have broccoli, brussels sprouts, and cauliflower. Can we remove those to see what an alternative omnivore diet might look like?
60g green peas
24g poppy seed
44g string beans
298g tomato paste
This diet uses 2514 Litres water per day. Yum, avocado! The green veggies got replaced with cabbage and zucchini. Eggs show up. But apparently leaving out the three magic green veggies has boosted the water usage quite a bit. Continuing this trend, if we omit cabbage and zucchini, they are replaced with celery and cucumbers, increasing the usage to 2786 Litres per day. I won’t bother showing it. If we remove celery and cucumbers, they are replaced with eggplant, okra, and soybeans, increasing the water to 2823 Litres per day. I think you get the idea.
Now let’s add some context. What’s the worst water usage I can come up with for a reasonable diet? Here we go:
50g lemons / limes
13g sesame seed
18g sunflower seed
That diet uses 20050 Litres of water per day. I’m not going to show the label because caloriecount.com is way off for the peppers, quinoa, and whey. Strange. Anyway, the peppers, plums, apples, and quinoa contribute the bulk of the water here because you can eat a lot of them. And this diet has a lot of them, which I capped at 1 lb each. Almonds show up, and they do use more water per gram, but you just can’t eat that many almonds without blowing your calorie and fat budget. Beef contributes more than the almonds here, as do the figs, flaxseeds, sesame seed, and whey. The other stuff is mostly just contributing nutrients and not so much water.
So far we’ve seen that purposefully mismanaging your diet can raise your water usage to more than 20 thousand Litres per day for food. If you’re paying attention, you can get it down to 2 or 3 thousand Litres. Now the real context: how much water do other daily activities consume? Let’s use the Personal Water Footprint calculator from waterfootprint.org. I entered zero for all the food and typical values for everything else, and I got roughly 2000 Litres per day. Wow, actually the food choices do have an impact.
I was surprised how often “bad foods” showed up in these optimized diets, like butter and palm oil. I think these foods are under-appreciated because people are making blanket statements about them, instead of considering the diet as a whole. Smarten up, people! Also, what’s the deal with molasses? I guess it’s the cheapest calories per water footprint, so it showed up a lot.
Some foods that we expected to show up did show up a lot, like broccoli, brussels sprouts, and cauliflower. Even in a drought, you can count on the classics.