Fundamental resources/Water

With world population growing, demand for food (and hence water for farming ) expected to grow by 70% ^[1], rivers becoming polluted and one in eight people already without clean drinking water ^[2], some have warned that we are heading for a 'peak water' crisis with people lacking the necessary water to survive, and wars breaking out over the access to water supplies ^[3].

A grim picture, indeed. But fortunately, an entirely avoidable one. Water is one of the most abundant resources available to us on this blue planet. The only problem we may face is synthetic scarcity; this article aims to show that there is no real shortage of water, nor of ways to purify and manage it.

Abundance of water

Over 70% of the surface of the Earth is covered by water, with the average depth of the oceans being 3.8 kilometres (12,430 ft) – we live on what is primarily a water world. Wasting the fresh water that falls on the surface of the land should of course be avoided wherever possible, but having enough fresh water in any place ultimately comes down to energy, rather than water itself — energy to transport water and energy to purify it.

As long as we have large amounts of renewable energy at our disposal (which we do - see the energy section), we can always create fresh water as required from seawater —

Desalination

97% of Spaceship Earth's water is in its oceans. Warnings of water shortages invariably dismiss desalination a priori as too expensive or energy-intensive ^[4][5][6]. Of course, ignoring 97% of a resource will make that resource seem really scarce. If the problem is that current methods of desalination are too inefficient, the obvious solution is to find better methods.

Currently desalination is done on a large scale with reverse osmosis  and membrane processes and these are indeed very energy intensive. However, as the energy article shows, we are not short on energy. But if we want a more energy-efficient means of desalination, solar desalination, nanofiltration and microbial desalination are promising technologies.

• Solar desalination  is a simple and ancient method of desalination that uses no electricity at all, just the heat of the sun to evaporate seawater, which seperates the salt from the water. It is only feasible in very hot countries, but these tend to be the ones most in need of water.
• Nanofiltration uses filters made of carbon nanotubes, small enough to let water molecules pass though, while blocking salt particles, impurities and pathogens. Nanofiltration uses only a quarter the energy of conventional methods of desalination^[7]. IBM are conducting research into nanofiltration-based desalination ^[8].
• Microbial desalination is particularly promising because, far from being energy-intensive, it actually generates electricity. It uses electrically active microbes to suck sodium and chlorine ions out of the water, simultaneously desalinating water and generating a flow of electrons.

How to get pure water

The intelligent use of mankind's water resources is not just an environmental issue; it is a public health issue. Drinking contaminated water is one of the most common causes of cholera, typhoid, diarrhoea, hepatitis A, dysentery and river blindness. Fortunately, using modern technologies, it is now possible to cheaply purify even the filthiest water — and even urine — into safe drinking water.

UV light is a clean and effective way to kill water-borne pathogens and requires no chemicals, only about 15W of electricity. As LEDs get cheaper and more energy-efficient, the use of UV-emitting LEDs to sterilize water becomes more and more attractive.

Suspended particles can be removed from water by passing them through a slow sand filter  with layers of gravel and sand. This is within the reach of all the World's people, as it requires no input of energy and no technological sophistication. A slow sand filter removes many, but not all, microscopic pathogens. The remaining ones can be removed by ultraviolet LEDs

It would be a relatively simple matter to fit homes with the means to catch rainwater, pass it through a slow sand filter and sterilize it with UV light. In all but the driest climates, this would provide the inhabitants of the home with an abundance of water. Decentralizing water-production would eliminate the need for a complicated water-grid and would make people more independent and resilient in the case of disasters.

Atmospheric water generators  condense water from the air. This water is clean and ready to drink. It is interesting to note that even very dry air contains about 5ml water per cubic meter of air, so even in a desert, you could condense enough water from the air to sustain a person or to grow food.

Nanofilters are an effective way of filtering out both suspended particles (which cause unpleasant tastes, smells and discoloration) and pathogens. The Tata Swach is a device that uses nanofilters to give very pure water. It retails for only $21.

Microbial fuel cells can be fitted to sewage water treatment facilities to generate electricity. One investigation found that the organic impurities in sewage contain 9.3 times as much energy as is needed to treat the water^[9]. It should be possible to integrate microbial energy-harvesting systems with water treatment facilities to create a self-sustaining facility that creates both clean water and clean electricity.

Using less water

In the USA in 2006, the average water use per person per day was 575 litres. Compare this with 149 litres in the UK and 4 litres in Mozambique. Peter Gleick has said that 50 litres of water is sufficient for a person^[10] and this is entirely feasible, without requiring sacrifices in lifestyle, just by improving system design.

Greywater  is the run-off from showers, sinks etc. It is water that has been used, but is not so dirty it cannot be used for purposes like gardening or washing clothes. Houses can be fitted with greywater recycling systems, where, for example, the output of the shower becomes the input of the dishwasher. This significantly reduces the amount of water needed to run a home.

Using composting toilets rather than flush toilets would save 26.7%^[11] of water use in the home. Composting toilets are also a source of fertilizer for growing food - and electrodes could even harvest electricity from the bacteria they contain (see Energy).

With the concern about conserving water in recent years, designers have developed toilets, sinks, dishwashers and washing machines that use a fraction of the water used by conventional designs.

However, reducing the domestic use of water is only a small part of the puzzle. Agriculture is the main cause of water use —

Agricultural water use

70% of world water use goes to irrigation for agriculture. Currently, the most commonly used method of irrigation is the most inefficient: flood irrigation. The single most important thing we can do if we want to reduce water demand is to increase the water-efficiency of agriculture. There are several very simple ways to do this —

• Ancient peoples living in dry places devised some ingenious systems to catch what little rainwater they had and use it to grow plants. This is exemplified in the area around Syria and Jordan, where there are productive rainfed farms in areas with as little as 120mm of rainfall per year.
• Drip and sprinkler irrigation can be used instead of flood irrigation. Drip irrigation is about 95% efficient ^[12][13], compared to about 50% for flood irrigation^[14]. The main barrier to implementing drip irrigation is a lack of proper equipment: but the trend towards distributed digital manufacturing will allow anyone to easily fabricate sprinklers, pumps, controllers and supply systems appropriate to their local needs.
• Aeroponics uses a tiny fraction of the water of drip irrigation. It is by far the most water-efficient means of growing food yet devised.
• Planting trees to provide shade for crops reduces the amount of water they lose through their leaves. This is an example of the synergistic use of different plant species typical of permaculture.
• Drought-resistant varieties of crops can be grown in water-scarce areas.
• Increasing water infiltration of the soil means less water has to be put in. Irrigating soil with poor infiltration is like trying to fill a bucket with a hole in it; when infiltration is increased, the soil holds water better and so less new water must be put in. One way to increase infiltration is no-till farming , which is gaining popularity around the world. Systems of permaculture that focus on building soil — with nitrogen-fixing plants, compost and other methods — will result in reduced need for irrigation.
• Large-scale atmospheric water condensers can readily be used to generate significant amounts of water from the air.
• Seawater agriculture can grow food in coastal regions, requiring no fresh water at all.

A combination of these techniques — applied intelligently and with a sensitivity to local needs and resources — can enable even rather dry climates to secure their own food supply without the need to pump in water from elsewhere. Rainfed agriculture currently provides about 60% of the world's food ^[15] and this could be expanded to much more using the methods mentioned here, while we can also make irrigation at least twice as efficient. This would massively unburden the world's water needs.