By Jeanne Yacoubou, MS

In a previous article, we calculated the carbon footprints of vegan pizza vs. meat pizza. The carbon emissions associated with the meat pizza were seven times greater than those resulting from the vegan pizza. In this post, we’ll see whether the difference between the water footprints of the same vegan and meat pizzas is as great.

Agricultural water use in a climate crisis

Approximately 70% of the world’s freshwater is used for food production every year. That is a huge withdrawal of the meager 3% total freshwater on Earth compared to saltwater (97%).

Compounding the problem of water availability is that only 0.5% out of the 3% is available for human use. (The rest is tied up in melting glaciers and polar ice caps, on their way to diluting salty oceans.) What is that quantity in gallons?

Based on estimations by the United States Geological Survey, in which the volume of all the freshwater on Earth is roughly 2,551,000 mi³ and one cubic mile of water equals more than 1.1 trillion gallons, the 0.5% of freshwater available for human use is approximately 2,551,000 x 0.005 x 1.1 ≅ 12,755 x 1.1 ≅ 14,031 trillion gallons ≅ 14 quadrillion gallons.

So, if agriculture uses 70% of the planet’s freshwater, that’s approximately 14,031 x 0.7 ≅ 9,821 trillion gallons ≅ 10 quadrillion gallons per year. That volume of water would fill roughly 9,821/660,000 ≅ 0.015 trillion ≅ 15 billion Olympic-sized swimming pools (holding 660,000 gallons each).

It makes sense in a climate crisis where global heating leads to extreme droughts or flooding in major agricultural regions to use that freshwater wisely. This is where foods’ water footprints can guide us to prudent water consumption.

What is a food’s water footprint?

The amount of freshwater (ground and surface water) needed to produce a particular food from farm to fork is called that food’s blue water footprint. In this post’s calculations, based on the work by Poore & Nemecek as interpreted by Our World in Data, only blue water, referred to as freshwater withdrawal, is counted.

The data used here do not include green water (rain/snow), or grey water defined as the freshwater needed to dilute pollutants – such as fertilizer and pesticide runoff – resulting from a food’s production to levels that meet local water quality standards. Nor do the data include where or when the water is used.

All types of water and where or when they are used are important in determining a food’s water footprint as accurately and precisely as possible. Other researchers consider all of these factors and more in their calculations of the water footprints of foods.

Water is used at every step of the process in food production including:

• Growing and harvesting crops
• Raising and slaughtering animals
• Processing all agricultural foodstuffs
• Packaging and transporting foods

Water footprints of pizza ingredients

Using Poore & Temecek’s data as presented by Our World in Data, we modified our ingredient tables used in our carbon footprint article to include water footprint data.

Vegan Pizza Ingredients

Total: 1,551.55 L ≅ 387.89 gallons

Meat Pizza Ingredients

Total: 2682.45 L ≅ 670.61 gallons

Conclusions about pizza water footprints

The water footprint of a meat pizza is 1.73 times higher than the water footprint of a vegan pizza. This result is similar to that of our 2017 assessment of the comparative water footprints of a bean/tofu burrito vs. a meat burrito. In that investigation, we found the water footprint of a meat burrito was 2.14 times as great as that of a bean/tofu burrito.

You may wonder why there is not a greater difference between the water footprints in our pizza and burrito examples like there was for carbon footprints (7-fold).

A 2020 review article on the water footprints of diets provides an answer to this question. In that meta-analysis, researchers noted that animal foods have significantly larger green water footprints while plant foods generally have larger blue water footprints.

Since our pizza example considered blue water footprints only, our final tabulation does not realistically quantify the total water footprint of the animal foods (beef, bacon, and dairy cheese) on the meat pizza. In other words, if both blue and green water footprints had been included, the difference between the water footprints of vegan vs. meat pizza – and, by extension, those of vegan vs. meat burritos – would be greater.

A.Y. Hoekstra, a leading water researcher, argues that the significantly larger water footprints of animal and dairy foods vs. plant foods have not been taken into account by nations overly concerned with sustainable production instead of sustainable consumption. Hoekstra points out that since raising animals for meat and dairy significantly adds to humanity’s water footprint, as well as to water pollution and water scarcity, countries searching for ways to save water must acknowledge that reducing animal products in our diet is an obvious solution and act on this fact.

In a world of increasing water scarcity in a climate emergency, every drop of water – green, blue, and grey – counts.

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