The best way to solve the world's water woes is to use less of it

And much of that has to do with agriculture

If the world is to reduce its use of water, the most obvious area in which to look for savings is where most water goes: agriculture. How much water this accounts for varies enormously from country to country. In Britain, which is a huge importer of embedded or "virtual" water (that consumed in producing any crop or product) accounting for as much as two-thirds of its waster needs, it is relatively little. In Egypt it is about 84%, and in India as much as 90%. Viewed more broadly, as a global water "footprint" - a concept developed by Arjen Hoekstra, a Dutch scientist - including not just the direct uses of water in agriculture, but the indirect ones all the way along the chain from field to fork, agriculture accounts for 92%. 

Much of this is wasted. "Flood" irrigation systems, where water is released to inundate fields or furrows, lose water to evaporation, or to percolation (ie, to the soil itself before it can be absorbed by the crop's roots). A common estimate is that flood-irrigation squanders 50% of the water it releases. Sprinkler systems can help with efficiency. But those, too, are imprecise, vulnerable to the wind and to loss of water through evaporation. 

Far more effective are "drip" irrigation systems introduced in Israel in the 1960s and since spread around the world. As the name suggests, these direct limited amounts of water to the plants themselves, so that they get enough but not too much. Avi Schweitzer, chief technology officer of Netafim, an Israeli company that sells drip-irrigation equipment and technology in 110 countries, says that, by minimizing both evaporation and percolation, it manages to achieve 95-97% efficiency in delivering the water to the photosynthetic process. 

This saves large amounts of water and increases yields. Precise amounts of nutrient and crop-protection chemicals can be added to the irrigation water. And the new generation of systems employ remote sensors that can monitor weather, soil and plant conditions and calibrate how much water is delivered. Mr Schweitzer, however, concedes that, for now, the high capital cost precludes the use of drip irrigation in much of the world, and limits its use to cash crops. The goals for the future are to reduce costs for commodity crops such as grains, and to improve precision even more. The market will expand. Climate change is likely to mean that more rain-fed - at present estimated to make up about 80% of the world's total - will be irrigated. 

Greater efficiency, however, comes with risks of its own: that farmers persist in planting thirstier crops than is rational in an arid climate, or switch to more water-intensive ones. Even in Israel, just south of the shrinking Sea of Galilee, swathes of irrigated land are covered in plastic-draped banana plantations. 

So reducing the water consumed by agriculture will depend not just on improving efficiency, but on rationalizing crop-planting. And that in turn will depend on demand and hence on changes in diet and even fashion. A foretaste of of controversies to come was a furore that arose last year over avocado-eating - criticized by many as an emblem of selfish millennial hipsterdom. Avocado consumption in America increased by 300% (to about 4.25bn avocados a year) from 2010 to 2015. Farmers scrambled to meet demand, including in very dry places, such as some parts of Chile and in Mexico, where the craze was blamed for a surge in deforestation. A kilo of avocados can need up to 2,000 litres of water, so local sources were strained, and activists mobilized to campaign against the culinary fashion. 

In future, people around the rich world at least likely to be made more aware of the water footprint of what they eat (and wear: the global average water requirement for producing a kilo of cotton is 9,359 litres). Avocados may need more water than tomatoes (214 litres) but they are far more frugal in their water needs than meat - chicken takes 4,325 litres per kg, mutton 10,412 and beef 15,415. Globally, however, the trend is not towards a low-water diet. On the contrary, as countries such as China grow richer, meat-eating is on the increase. Over the past 50 years, global meat production has quadrupled. 

Another way in which water is used inefficiently in agriculture is in waste or loss of food, which adds up to as much as a third of global production. In countries such as India, the inadequacies of the cold chain and logistical hurdles mean that much never reaches the shops. Even in rich countries, food shops and consumers end up discarding vast amounts of uneaten food. 

A new report by the World Economic Forum, a think-tank, emphasizes technological fixes to this problem. Sell-by^[각주:1] and use-by dates^[각주:2] could be replaced, it argues, by remote sensor technologies, such as near-infrared spectrometeres and hyperspectral imaging, capable of evaluating the perishability of individual items. It looks forward to the day when the imaging technology is available on shoppers' smartphones. 

A less visible but perhaps more shocking waste is in the form of "non-revenue water" - that is, water supplied by utilities but never paid for. Some is diverted and stolen; much is simply lost through leakage. The lost revenue often leads to a vicious circle. Money is too short to maintain and repair the system, leaks increase, pries rise and theft becomes more widespread. The problem is most obvious in poor countries. Delhi's water board, for example, reported in 2011 that 53% of the water it distributed was non-revenue. In Hanoi that figure was 44%. But even in the rich world, where pipes and other infrastructure may be old, rates can also be staggering. London, for example, reported 28% and Montreal 40%. Again, technology is helping. Sensors and smart valves that use the water itself to send a pulse, which alters when there is a leak, can make it easier to pinpoint trouble-spots. 

In almost every aspect of water usage the scope for using less is enormous. It is a question of incentives. Optimists point to signs that this is changing. Some governments still use the availability of cheap and plentiful water as a lure to foreign investors. But some businesses are seeing water-efficiency as both an economic goal in itself and as an important part of their image-building. In the Canadian province of Ontario, for example, the local arm of Nestlé, a Swiss-food-and-drinks giant that is one of the world's biggest sellers of bottled water, has found itself embroiled in a lawsuit between^[각주:3] First Nations representatives and the provincial government, which has led to a moratorium on issuing new bottling permits. 

Elsewhere, Nestlé is making much of its efforts to save water, aiming to reduce usage in every product category between 2010 and 2020 (a target it says is already within touching distance). In some countries, for example, such as America, Brazil and South Africa it makes baby milk in "zero-water" factories, reclaiming water evaporated from cow's milk used in the manufacturing. 

Unilever, another multinational, also has set "sustainability goals". One is to keep the water used in its manufacturing processes to 2008 levels, despite greatly increased production. Already, it says, it has cut water use per tonne of production by 39% since 2008 water-scarce countries^[각주:4] representing half the world's population. Less successful has been its drive to reduce the amount of water its customers use - by making products, such as detergents, for example, that need less water. Since 2010, per-consumer use has fallen only by 2%. 

1. sell-by date (英) (美 ˈpull date) ; [명사] (상품의) 유통 기한 ;; [NOUN] The sell-by date on a food container is the date by which the food should be sold or eaten before it starts to decay. ;; This label is aimed retailers, and it informs them of the date by which the product should be sold or removed from shelf life. This does not mean that the product is unsafe to consume after the date. Typically one-third of a product's shelf-life remains after the sell-by date for the consumer to use at home. [본문으로]
2. [/footnote][footnote]use-by date ; (보건) 소비기한(消費期限) ;; This label is aimed at consumers as a directive of the date by which the product should be eaten; mostly because of quality, not because the item will necessarily make you sick if eaten after the use-by date. However after the use-by date, product quality is likely to go down much faster and safety could be lessened. [본문으로]
3. embroil ; [타동사][VN] [흔히 수동태로] ~ sb/yourself (in sth) (격식) (언쟁 등에) 휘말리게 만들다 ;; [VERB] If someone embroils you in a fight or an argument, they get you deeply involved in it. ;; 미국∙영국 [ɪmˈbrɔɪl] [본문으로]
4. water-scarce ; 물 부족 [본문으로]