Ruth Matthews, executive director of the Water Footprint Network, tells Tom Levitt how food has come to dominate our water use and why China may need to re-think its South-North water transfer project.
Tom Levitt: What do you mean by our water footprint?
Ruth Matthews: A water footprint generally breaks down into three components. The green water footprint is the water that is used by plants from rainfall that has not run-off the soil and is taken up by crops. The blue water footprint is water that has been withdrawn from surface or groundwater and used in industry or agriculture. The grey water footprint is the amount of water necessary to dilute polluted water to meet water-quality standards.
TL: Which sector has the highest water footprint?
RM: Agriculture has the highest water footprint, accounting for 92 percent of the blue water footprint. You might have heard figures of 70 percent to 72 percent for agricultural withdrawals of water, but what we’re looking at is the water that is actually consumed and including green water footprint, which explains why agriculture uses up more than 90 percent of the water footprint of humanity.
Industry may withdraw a significant amount of water but a good proportion of that is not evaporated or incorporated into the product and is just returned to the source. For example, power-generation stations use cooling water but that water is not lost or consumed. Whereas water taken up by plants and evaporated or incorporated into, for example, a juicy watermelon, is now unavailable for other uses.
TL: Can you explain the problem of meat and its high water footprint?
The Water Footprint Network estimate that the average water footprint per calorie for beef is twenty times larger than for cereals and starchy roots. With the biggest contribution coming from growing their feed. In the U.S., for example, 68 percent of the grains produced are used for animal feed.
RM: There has been a study done, specifically in China, looking at how as the economic wealth of people grows, the consumption of meat is rising even more quickly. What that means is there is more pressure to either produce internally or to import meat products. Meat is a very high consumer of water, especially if you consider what is going into the feed. In some cases that feed is natural grassland and rainfed so the amount of water that is being put into it is not necessarily having an impact on the blue water resources. But if we are using that rainfall to grow soybeans to be eaten by cows to create beef, then we are getting less protein out of that rainfall than if we grew soybeans that were then eaten directly for their protein source. We are creating an additional food inefficiency in our food system.
TL: How are water scarcity issues likely to impact on U.S.?
RM: The reality is that developed countries significantly externalize their water footprint. For example 42 percent of Europe’s water footprint is overseas. In some European countries the figure is even higher. What that means is that there is a relationship between the citizens of the EU and river basins around the world. As a country looks at how it manages its own water resources, you could suggest that it has the same responsibility to help the management of water resources in other river basins and meet those high standards of protection. In developing countries where there is less strict regulation, less capacity for monitoring and enforcement of those regulations the agriculture is done in such a way that there isn’t much protection for water.
Countries like China and the U.S. are in an interesting situation as they have a significant amount of natural resources themselves because they are such large countries. The amount of water the U.S. imports and exports is fairly close, so it is putting a burden on other countries but is also relieving the burden because it is exporting goods, such as wheat.
TL: What are your views on China’s water footprint?
RM: What’s interesting in China is that for various reasons, including political, they have developed a lot of the agriculture in the north where it’s relatively water scarce. Within the country there is now a virtual water trade from the north to the south, which is fairly water rich. They are overtaxing water resources in the water-scarce north to transfer food to the water-rich south.
And now they are looking at doing a massive water transfer from the south to the north to help support Beijing’s water and also to provide water to agriculture that is in the north. From an economic and environmental sense it’s irrational. It doesn’t make sense to push your agriculture in the north when you’ve got a lot of water in the south but this is how the situation is there now.
As China’s population grows they are looking at more dependency on external water resources. So as well as looking at their internal water footprint, they have an opportunity to either take the proactive step of helping those countries where they are reaching out to use water resources in a sustainable and equitable way or instead contribute to the continual degradation of the river and groundwater ecosystems.
See: Water transfer projects “essential” says Chinese scientist
TL: What can we learn from water footprints?
RM: One of the things we can do with our water footprint assessments is to understand how water is being used within individual river basins and how that relates to the amount of water that is available and the amount that needs to stay in the river or aquifer to sustain biodiversity, ecosystem services, and subsistence uses of water. What we see is that in certain times of the year in many river basins, because the amount of water that is available is less than is being used for agriculture and other uses, you see high water scarcity.
One of the things we can do to improve food security is to really make the most and smartest use of green water resources. We can take some of the pressure off our blue water sources—lakes, rivers, and aquifers—by increasing the efficiency of our use of rainfall and so reduce the green water footprint. This means that we are producing more food with less rainfall and by doing that you can also reduce the amount that you are dependent on those blue water resources.
If you look at the amount of green and blue water footprints needed for growing cotton in places all over the world what you see is that the countries around the Aral Sea in general require a much higher blue water footprint than other places because there is so little rain. The result has been the virtual disappearance of the Aral Sea and loss of fisheries from a massive growth in irrigated agriculture. So if you are going to be growing a very water thirsty crop, which cotton is, a really smart thing to do is to grow it in places where there is a significant amount of rainfall—reducing your reliance on blue water resources to the smallest amount possible.
TL: What are the best solutions to reducing our water footprint?
RM: For the private sector it is for there to be accountability in supply chains. So if a company like Unilever is selling all different types of products, they are not just looking at their operational footprint but also the water footprint in their supply chain, making sure that they are taking action to improve the sustainability and equitability of that footprint. In the public sector, it would be for the government to bring water footprint accounting into the mix of what they track, in the same way as they record GDP and trade exports and imports.
Water footprint accounting can help them understand how water is used within the country—the sectors using it and the products produced as well as their economic value. Furthermore, how much water they are importing through virtual water flows and the value of that and how they are connected to water scarcity and pollution hotspots both within the country and externally.