Saturday, August 23, 2008

How large is your water footprint?

Planetary supplies of fresh water are becoming more and more scarce as demand from six billion people on earth keeps soaring. Partly this is because world population continues to explode and many of its inhabitants are getting richer and and thus expanding demand. In other words it's the old story all over again that I explored in my 'food' posts - India and China are to blame! Be that as it may, and it may well be true, it is indeed a fact that water supplies are dwindling. Rivers such as the Nile, the Yangtze, the Jordan and the Ganges regularly peter out during the summer months and the water table in major cities like New Delhi, Chennai, Beijing and others have fallen drastically. Here are some little known facts which would help to put the problem in perspective. On an average, according to the Stockholm International Water Institute, on average each person on earth uses 1000 cubic meters (m^3) of water per year. A cubic meter being a 1000 litres, this works out to one million litres of water per year per capita! Now, before you think I, or the gentlemen at the institute above have been indulging in some vapourous stimulants to come up with such outrageous numbers, let me explain what these numbers mean. This is the average water footprint of each person on earth i.e. this is all the water we use for drinking, hygiene, growing food and all other activities. Or in other words, the water footprint of an individual, business or nation is defined as the total volume of freshwater that is used to produce the goods and services consumed by the individual, business or nation. It is then easy to understand the magnitude of these numbers. A kilo of beef needs 16000 litres of water (for grain fed cattle and therefore not true in India). a kilo of wheat or corn requires about 1000 litres for irrigation, even a cup of coffee requires around 140 litres of water to grow the requisite number of seeds to make that coffee. The actual drinking water that the metropolitan supply delivers to our homes (or, as in Chennai, more often than not, does not deliver) is a minuscule fraction of our total water footprint. The water footprint could also include items like a cotton shirt (which has a virtual water content of about 2000 litres). Consequently, an individual's water footprint is also dependent in many ways on his/her prosperity level. India's average water footprint per year per capita is around 980 cubic meters not very different from the world average. You can also calculate your individual water footprint from this site. For an average meat eater in India, this works out surprisingly to around 540 cubic meters per year, of which something like 520 is for food and 18 is for domestic use (this is the part which is actually supplied to our homes). Of this 520 for food, in India, almost 90% is for cereal consumption, the meat contribution being negligible. The same parameters including annual incomes applied to the US produces a number of around 1200, about 80% of which is from meat consumption. The difference in India between vegetarians and non vegetarians is in fact negligible. If anything, the vegetarian water footprint is marginally higher, presumably due to higher grain consumption. These and many other interesting facts can be discovered by playing with the water footprint site calculator given earlier. Which begs the question -- if most of us have a water footprint of around 500, why is that of the country around a 1000. Which part of the population is tilting the balance to such high numbers? Here are some other interesting facts which you can find from the papers linked at the site. For example, with regard to the water footprint of nations, in absolute terms, India is the champion -- 987Gm^3/year. Even though India's population is 17% of the world's, its people contribute only 13% to the global water footprint. On a per capita basis, the US is the champion -- 2480 m^3/year/capita followed by people in Southern European countries. On the other hand, despite our tendency to blame China's growth for most developmental problems, China has a much smaller footprint -- around 700 m^3/year/capita. However, as with many consumption patterns, India (13%), China(12%) and the US(9%) are the largest consumers of the global water resources. Interestingly, Japan's external water footprint ratio to the total footprint is very large (65%) compared to the three countries above (1.6% for India), mainly because it imports a large number of agricultural and industrial products. An interesting aspect of this external footprint is that, by importing say rice and other grains from another country with higher productivity per acre, we are actually reducing our own water footprint and making more effective use of water. Sources of water Finally, where is all this water coming from? All the fresh water on earth comes from precipitation. Of this, 61% is what is called Green water that flows through the landscape and is absorbed by soil and plants and is not available for direct withdrawal. About 38% is called Blue water and collects in rivers, lakes, wetlands and groundwater and is available for withdrawal. Irrigation from this blue water is the largest single use of freshwater (1.4% of the total), with cities and industries consuming a tiny fraction of the total usage (.1 %). However, this tiny usage actually creates a large local demand, thus draining nearby regions of ready supplies of fresh water as we have seen happen in India. Finally around 1.3% is lost through evaporation. In a future post, I will discuss what we can do (both individually and as a nation) to reduce water consumption. For those of you interested in reading some more, the August 2008 issue of Scientific American has an article on Water. The Water Footprint site mentioned in my post above is a rich resource for water related issues.


AMOK said...

This is a great topic -- especially since this blogger was recently traveling among and between some of the largest fresh-water bodies on earth. Need more time to absorb the blog contents, though. Perhaps about 2000 litres worth of time. Like a standard enthalpy of formation. Any idea what the water footprint is of one litre of potable water? Obviously it is not 1 litre. Can all units be reduced to water(y) units, Sire?

AMOK said...

This blogger is still catching up with blogs owing to a time away from keyboards (but not in Singapore). The laws of conservation of energy seem not to apply to energy, though. Nuclear energy was hyped as "too cheap to meter". Solar energy is a "clean energy". Today, no one is asking "what is your natural gas footprint?" in Utah. I wonder if CNG is too cheap to meter, so to speak? Used without planning, it too will have the same problems and issues as other petroleum products. What is the total energy profile (and hence population) our planet can process efficiently, per energy source? Kindly put forward a grand, canonical equation for this, Sire, while you are working on the water footprint.