08 August, 2007

Where does water go?

A friend of mine has recently suggested that at least some of the water shortage our civilization experiences may be caused by the fact that our bodies consist mostly of water and, as the population grows, more water gets trapped. Let's see how much water can get statically bonded -- not only in human bodies, but in other civilization-related containers.

  • Human bodies. With about half of the body weight being water (en.wikipedia.org/wiki/Body_water) and assuming the average person weight of 60kg (with Americans being averaged out with Vietnamese), our mortal shells hold 6*10^9*0.03=1.8*10^8 cubic meters of water in total.

  • Public Water Supply. If there is a 4cm pipe at least 10m long per each (of the, say, 2 billion) persons who have running water in their homes, then we'll have 2*10^9 * 10 * (2*10^-2)^2 * 3.141592 = ~0.24*10^8 m^3 of water. At least the same amount of water lurks in inter-house pipes, so we get 0.5*10^8 m^3 in total

  • Toilets. With 4 liters per tank and assuming one toilet per each person of those 2 billion (public/office restrooms may drive this figure even higher), we get 8*10^9*10^-3 =~ 0.1 * 10^8 m^3 [Hmm, not too much. I was expecting a tad more.]

  • Cattle. 1.3 billion heads (cattle-today.com/), 400kg each, assuming the same water content as humans, and assuming most of the population is a direct product of our civilization, 1.3*10^9*0.2=2.6*10^8 m^3.

  • Piggies About a billion, say 200kg each, 10^8 m^3 of water.

  • Pets Say, 200 million dogs, 10 liters each, on average, and same number of cats, 5 liters each: 300*10^6*0.01 = meager 0.03 * 10^8 (less than in toilet tanks!)

  • Agriculture 14 billion tonnes of "stuff". I assume this includes watermelons/tomatoes/oranges/etc. -- which consist mostly of water. But, being conservative let's assume it is still a half, so 7*10^9 = 70 * 10^8 (aha!)

  • Beverages Beer, ~120*10^6 m^3 per year, so, assuming there's always a 10-day supply in storage, 120*10^6 / 36 =~ 3 * 10^6. Juices and wine being included in Agriculture, let's suppose consumption is the same for carbonated non-alcoholic drinks (Coca/Pepsi-Colas, etc.) -- another 3*10^6. Milk -- 300*10^6 annual production, under the same assumption as for beer/sodas, 10*10^6 m^3 of static water. In total, about 0.2 * 10^8 m^3 of water is kept in beverages.

  • Cars [fetched the manual] About 7 liters of coolant + a liter or two for windshield washing. 6*10^8 cars, 0.06 * 10^8 m^3. meh

  • Other containers: Blood donation in the US are 15*10^6 of half-liter units annually, so it isn't that much static water. Ice rings or pools (especially the Olympic-sized ones) -- may be quite a bit of water, but they aren't many. What else... poultry? Well, doubtfully more than in pigs.

    Lots of water is used in paper production, but I would assume not much of it ends up in paper. Paint and Perfume may be worth looking into, but I doubt there's more water in paint than in beverages. Potentially, a lot of water may be held in bodies of domestic cockroaches, miscellaneous agricultural pests, lab mice, etc., but doubtfully it will increase the final figure by more than twice.

    In conclusion, the amount of water held by the civilization statically is about 10 cubic kilometers. Which could power the Amazon river for about a day!

    On the other hand, lake Baikal holds 23.5 thousand cubic kilometers of fresh water (20% of world supply). Must. Grow. More. Pigs!
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