Water, pollution and food: from aquifers to dead zones

Three kinds of water, one honest accounting

Green water is rain; blue water is irrigation and groundwater; grey water is the volume needed to dilute pollution. Headline animal-agriculture figures are often dismissed as 'mostly rain', but blue and grey water alone still favour plants by a wide margin, and it is blue and grey water that empty aquifers and poison rivers.

Aquifer depletion has a feed problem

In the High Plains of the United States, a large share of Ogallala pumping irrigates feed corn and alfalfa. Similar patterns appear in northern India, the Iberian peninsula and northern China. When aquifers fall faster than they recharge, the water is not being borrowed — it is being spent.

Nutrient pollution and dead zones

Concentrated animal operations produce more manure than nearby land can absorb. Nitrogen and phosphorus reach waterways, feed algal blooms, and the decay of those blooms strips oxygen. The result is hypoxic zones where fish and invertebrates cannot survive, recurring annually in the Gulf of Mexico, the Baltic and the East China Sea.

• Ammonia emissions from manure also drive fine-particulate air pollution linked to premature deaths.
• Antibiotic and hormone residues enter watercourses alongside nutrients.
• Communities near large operations bear health and property-value costs the market never prices.

What changes when diets change

Modelling of national diet shifts consistently reports double-digit reductions in blue-water use and larger reductions in eutrophication potential, because plant foods skip the feed-conversion step where most water and nutrient loss occurs.