For Parched Times, a New Water Calculus

A worker at a mill in Amravati, India, soaks bales of cotton with water before they are taken for cleaning and processing.

In my article about efforts by Levi Strauss & Company to adapt to climate change by reducing its water consumption, I mention the company’s estimate that each pair of 501 Levi’s jeans will consume 919 gallons of water during its life cycle. That includes everything from irrigating the cotton crop, to rinsing the jeans during the manufacturing process, to lots of home launderings.

But do those measurements go far enough?

It turns out that measuring water use is just as tricky as measuring carbon dioxide emissions. Yet the Water Footprint Network, a nonprofit group based in the Netherlands, has developed what it calls a gold standard for water use measurement and is urging that it be embraced by corporations, nations and individuals.

The method involves a calculation of “blue water” – that is, the amount of fresh water a company extracts from, say, a reservoir, a stream or an underground aquifer.

But the group also factors in categories that are less obvious. It counts “green water,” for example, or precipitation that falls but does not recharge groundwater or streams because it is absorbed for other purposes like growing cotton. And it measures “gray water,” or the water used to dilute pollutants in a manufacturing process so that they do not harm the local water quality when they are discharged from the factory.

Needless to say, this approach significantly increases the water footprint of any product or activity.

For one kilogram (2.2 pounds) of cotton, which is roughly what goes into a pair of jeans, only 33 percent of freshwater use comes from irrigation. Gray water accounts for 13 percent and green water for a stunning 54 percent.

Brian Richter, director of global fresh water strategies for The Nature Conservancy, a global nonprofit group that is trying to disseminate the more comprehensive standard, says the most common measurement simply factors in the blue water. Even federal agencies like the United States Geological Survey only track blue water in measuring water use, he said.

Yet as global awareness grows that a shortage of water resulting from drought and climate change could pose major business risks, he said, corporations are paying more attention to what is used throughout their supply chains.

“Companies are asking, ‘is there enough water available for our operations? Will it cause us to be blamed if there is not enough left in local environments?’ ” Mr. Richter said.

Measuring blue, green and gray water use gives a company a clearer idea of where problems within a watershed could develop, he said. As a result, more companies are beginning to count all three.

Ideally, Mr. Richter said, those numbers should be broken down. “It is really more interesting and most effective to keep those numbers separate, because if you combine them, the agglomerated number is hard to understand,” he said.

In the end, the numbers “aren’t really the issue,” he said. “It’s the question of whether or not the use of water is causing problems for other people, or the environment.”