In the 1955 film ‘The Dam Busters’ aeronautical engineer Barnes Wallis explains that to make a ton of steel, the Nazis require a hundred tons of water. Thus the dams of the Ruhr valley become the target of a new weapon, the iconic bouncing bomb.
Nowadays, targeting a dam would be a war crime, but for us it’s a memorable way to introduce the concept of embodied material: things that are used up in order to create something, even though they don’t feature in the end product. This issue renders highly inaccurate any attempt to measure the environmental impact of a product by simply dismantling it and identifying the material of each component part.
Which brings us, of course, to the cucumber.
When you buy a cucumber, you’re also paying for about 140 litres of water… or somebody is. Now, a cucumber is mostly water, it’s true… but even if a typical 400g cucumber was 100% water, that still leaves approximately 139.6 litres of water that you don’t see. What happened to it? Quite a bit of it leaked away or evaporated before it ever reached the root system of the cucumber plant. Transpiration – the loss of moisture from the leaves, stems, or flowers – accounts for much of the rest, and a little of it was turned into carbohydrates by photosynthesis…
This website provides information on the ‘water footprint’ of a range of products, and the implications are startling. Water consumption is expressed in litres per kilogram of end product. For cucumbers (and pumpkins) it’s 350 litres per kilogram.
When we’re in the supermarket, and we select a cucumber that was grown in, say, Turkey (the third largest producer, at a little over 1.7 million tonnes of the things per year), we might do well to remember that 350:1 ratio. In exchange for some small fraction of the purchase price of a 400g cucumber, the typical grower needed almost a seventh of a tonne of water.
When you consider the geography of our planet, water doesn’t seem all that scarce – and it isn’t – but only 2.5% of the world’s water is fresh. The oceans account for virtually all of the rest, and they are too salty for growing crops. Of the 2.5% of water that is fresh, a massive 68.7% is locked up in the ice caps, or in glaciers elsewhere. 30.1% more is beneath the ground, and requires boreholes or wells (which themselves aren’t free from problems, long-term). That leaves just 1.2% of the world’s fresh water actually available on the surface… but 69% of that water is tied up in permafrost. (All figures from the US Geological Survey.)
Basically, the amount of water available for immediate use by humans and animals is tiny – and it isn’t evenly distributed. Last time I looked, fresh water wasn’t all that abundant in Turkey. Extraction of groundwater in order to grow crops might seem to be a bargain; simply borrowing it from the substantial 30.1% of all fresh water that resides under ground… but the resulting lowering of the water table can render present-day wells useless, and cause subsidence or seawater intrusion.
There is really only one piece of good news to be found in the study of embodied water, and that’s if you’re a drinker: beer and wine are relatively ‘inexpensive’, so you can feel that you’re doing your bit for the planet every time you choose to have a glass, instead of reaching for a burger, or a bar of chocolate.
And if you really want to be ‘green’… there’s always cabbage.