Water use
Water footprints explained
The figure for a kilogram of beef or a cup of coffee is a global average that mixes rainfall with abstracted water. Useful, and routinely over-read.
Water footprint figures — 15,000 litres for a kilogram of beef, 140 litres for a cup of coffee — circulate widely. They come from real research, and they are almost always presented without the three qualifications that determine what they mean.
The three colours
- Green water
- Rainfall consumed by a crop as it grows. It was never abstracted from a river or aquifer, and in a rain-fed system it would largely have evaporated anyway.
- Blue water
- Surface or groundwater abstracted for irrigation and consumed. This is the water that competes with other users, and it is the number that matters for scarcity.
- Grey water
- A theoretical volume of water that would be needed to dilute pollution from production to acceptable concentrations. No such water is actually used. It is a pollution indicator expressed in volume units.
| Product | Total footprint (litres/kg) | Note |
|---|---|---|
| Beef | ~15,400 | Dominated by feed crop green water; varies enormously between grass-fed and feedlot systems |
| Sheep meat | ~10,400 | |
| Pork | ~6,000 | |
| Chicken | ~4,300 | |
| Cheese | ~5,600 | |
| Nuts | ~9,000 | Almonds in irrigated arid regions have a high blue water share, unlike most of this table |
| Rice | ~2,500 | High blue water share where irrigated |
| Wheat | ~1,800 | |
| Cotton (fibre) | ~10,000 | Historically the driver of the Aral Sea diversion |
| Coffee (roasted) | ~18,900 | Roughly 140 litres per cup |
| Chocolate | ~17,000 | |
| Milk | ~1,000 | Per kilogram |
| Vegetables | ~300 |
Global averages from the Water Footprint Network reference dataset, for a 1996–2005 period. Regional values vary by more than an order of magnitude, and these are not measurements of any particular product.
Table sources
- Water Footprint Network — Water footprint of crops, products and nations. Open — attribution required · CC BY 4.0
What the numbers are genuinely good for
- Comparing broad categories: animal products consistently require far more water than plant products, and that conclusion is robust across methods
- Identifying where blue water pressure is concentrated — irrigated cotton, rice and almonds in arid regions are genuinely water-intensive in the way that matters
- Understanding virtual water trade: importing food is importing the water used to grow it, which is how water-scarce countries function at all
What they are not good for
- Assessing an individual product. Rain-fed beef in Wales and feedlot beef in an irrigated arid region have very different footprints and the same global average
- Implying that reducing consumption of a high-footprint food frees up that water for other uses. Green water is location-specific and mostly not transferable
- Comparing across regions using a global average, which is what most published comparisons do
Sources
- Water Footprint Network — Water footprint of crops, products and nations. Open — attribution required · CC BY 4.0
- International Organization for Standardization — ISO water quality and water footprint standards. Permission required · ISO copyright — standards sold per document
- Food and Agriculture Organization of the United Nations — AQUASTAT — Global Information System on Water and Agriculture. Public but restricted · CC BY-NC-SA 3.0 IGO