How wet is your cucumber?

There are many arguments about the effects of our food consumption. In particular, the consumption of meat is often portrayed as harmful, be it for the climate, for food supply or for our health. What we eat and how we process it effects water consumption, here the concept of water footprint is the most used. Treehugger says that if you really want to reduce your water foot print you should cut back on meat. The Guardian calls for water foot print labelling. 

While a human being needs a few litres of water to drink, at least 1000 times as much water is used for production of food. The water needed for foods varies tremendously and varies for the same product under different conditions. Often the figures mix  ‘blue’ water—water in rivers and lakes, ‘green’ water—water in rainfall and in the soil, and ‘grey’ water—the water needed to absorb or purify the waste. The water footprint - per kg - of beef is big, ten times as big as for grain and fifty times bigger than for vegetables, if water sources are counted.

	Water use (l/kg)
	Green	Blue	Grey	Total
Beef	14414	550	451	15415
Nuts	7106	1367	680	9153
Lamb	8253	457	53	8763
Ckicken	3545	313	467	4325
Egg	2592	244	429	3265
Oil crops	2023	220	121	2364
Grains	1232	228	184	1644
Milk	863	86	72	1021
Root crops	327	16	43	386
Vegetables	194	43	85	322
Sugar crops	130	52	15	197

But statistics can be presented in many ways. Green water as rainfall is not the same as the water in lakes or wells, the blue water. In many places where cattle graze it would still be too dry to grow any crop. Also, water foot print per kg is a dubious measurement. We eat very different quantities of food, and their concentration of useful nutrients differ widely. If we look at use of blue and green water per calorie, nuts has the lowest efficiency in water use and root crops are the best. Vegetables and meat are quite similar.  Looking at blue and grey water use per protein, oil crops are best followed by milk, lamb root crops and grain. Nuts and vegetables are the least efficient.  

In general many people jump to conclusions when it comes to food. Mostly, they jump in the direction of a choice they already made.