Why sell food when you can sell water?’ asked a 1980s ad against food adulteration. Since food is sold by weight, and water is weight, the more water one could inject into food, the greater the profitability. A policy tussle ensued as Trading Standards officers and consumer advocates such as the London Food Commission tried to restrict practices such as ‘double-glazing’ frozen foods and other semi-legal methods of flogging water as food.

I pondered water’s role in food last Sunday, which was World Water Day. Blink and we missed it. I was tending my surprisingly dry London vegetable patch, thinking how the food-water connection will be big news even in wet Britain in coming decades. Water won’t just affect profits; it’ll affect life itself. Three papers from the UK Global Food Security champion due soon make the point. As one expert told me last week: forget how much water you use in washing-up, it’s your food, stupid! Would labelling foods for water content help? No. Dietary change is what matters.

“A kilo of US beef uses as much as 15,000 litres of water”

Globally, 70% of all potable water is used by agriculture, most of it for irrigation. And if you think that only occurs in arid regions, think again. It affects Eastern Britain already. Discussing ecosystems in Vienna this month with UN analysts, we agreed food and water stress is a key indicator, even before climate change kicks in.

Diets alter with rising living standards. People consume more food of higher ‘embedded water’, such as meat and dairy. A kilo of US beef that the TTIP trade deal may be bringing our way uses as much as 15,000 litres. The basmati rice we eat with our British curries actually uses 3,500 litres of water for each kilo of rice. And that’s before you even cook it. 

Since UK water utilities were privatised and began big infrastructural investment, everyone’s water bills have risen. This has incentivised water use reduction. Indeed, a 2013 study by Wrap found the UK food sector, post-farm, using slightly less water since 2007. Don’t be fooled. This is not the point. As tastes change, water use goes up inexorably. When the OECD estimates 47% of the world will be water-stressed by 2050, be concerned. Low water use will be a key feature of sustainable diets. 

Tim Lang is professor of food policy at City University London