A cotton T-shirt takes roughly 2,700 litres of water to produce, about what one person drinks in two and a half years, and most of that water is pulled from irrigation-stressed river basins in Central and South Asia thousands of kilometres from where the shirt is eventually sold

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A single cotton T-shirt takes roughly 2,700 litres of water to produce, which is close to what one adult drinks in two and a half years at the standard eight cups a day. Most of that water never touches the shirt. It falls on a cotton field months earlier, in a river basin thousands of kilometres from the shop where the shirt ends up folded on a shelf.

The number is a life-cycle estimate, not a factory reading. It bundles rainfall, irrigation, dyeing, finishing and transport into one figure. The bulk of it — around 90 percent in most published assessments — is agricultural water absorbed by the cotton plant itself.

And cotton is thirsty in places that can least afford it.

Where the 2,700 litres actually goes

The figure traces back to work by the Water Footprint Network in the late 2000s, which broke a cotton shirt down into three water categories: green water (rainfall used by the crop), blue water (surface and groundwater diverted for irrigation), and grey water (freshwater needed to dilute the pollution from dyes and finishing). Only a small fraction of the total is the water that gets a shirt clean, dyed and shipped. The overwhelming share is what the plant drank in the field.

A mid-weight cotton tee contains around 250 grams of lint. Growing that lint requires around a kilogram of raw cotton bolls, which in turn requires the plant to be watered for roughly 160 to 200 days depending on the variety and climate. In an unirrigated field in a wet region, most of that water is rain the sky was going to deliver anyway. In an irrigated field in a dry region, it is water pumped from a river or aquifer that was doing something else — feeding a wetland, recharging a well, supporting a fishery.

The environmental accounting the industry cares about is the second kind.

The starkest illustration sits between Uzbekistan and Kazakhstan. The Aral Sea was the fourth-largest lake on Earth in 1960. By 2014, satellite imagery showed its eastern lobe had disappeared entirely. Soviet-era irrigation canals diverted the Amu Darya and Syr Darya rivers to feed cotton fields across Central Asia, and the sea they had drained into for millennia simply ran out of inflow. Uzbekistan remains one of the world’s largest cotton exporters. The country’s cotton is grown on land that would be desert without pumped irrigation from those same two rivers, which now deliver only a fraction of their historical flow to what is left of the sea.

India and Pakistan tell a slower version of the same story. The Indus basin, which supplies cotton mills across Punjab and Sindh, is one of the most groundwater-stressed river systems on Earth. Tube wells across the Punjab plains have dropped water tables by several metres over the past two decades. Cotton is not the only crop pulling on that water — rice and sugarcane are also intensive — but it is a significant share, and its water leaves the basin embedded in fabric shipped abroad.

Virtual water and the distance it travels

Economists call this virtual water: the water embedded in a traded good, moved from one country to another whenever the good is sold. When a shirt sewn in Bangladesh from Uzbek cotton is bought in Berlin, roughly 2,700 litres of Central Asian irrigation water has effectively been exported to Germany. The shirt weighs 150 grams. The water it represents weighs about 18 tonnes.

Global trade in cotton and cotton products moves an estimated 200 cubic kilometres of virtual water a year across borders. That is roughly four times the annual flow of the Colorado River.

The shirt on the shelf carries none of this on its label.

The dye house is the other half of the problem

The 2,700-litre figure includes water used in dyeing and finishing, and that fraction is small in volume but disproportionate in damage. Textile mills in Bangladesh, India, China and Vietnam use freshwater to fix dye onto fibre, then discharge much of it as effluent. A single kilogram of finished fabric can require 100 to 150 litres of process water, and untreated effluent from dye houses is one of the reasons some rivers in South Asia and southern China visibly change colour by the season.

The Buriganga in Dhaka, the Citarum in West Java, and stretches of the Pearl River delta in Guangdong have all been documented running the colour of whatever is being dyed upstream. Grey water accounting in the Water Footprint Network method tries to capture this by asking how much clean water would be needed to dilute the pollution back to safe levels. For a conventional cotton shirt, that dilution water is a significant slice of the total.

The industry as a whole uses around 79 billion cubic metres...