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Water scarcity – solving it one drop at a time

Dr Tim Fox, Food and Drink Engineering Committee

Half of the countries of the world facing water insecurity issues and outright shortages by 2025
Half of the countries of the world facing water insecurity issues and outright shortages by 2025

It is estimated that in the world today, about 2.8 billion people are subject to conditions of moderate to severe water scarcity for at least one month of each year. Many of these live in the poor rural communities of developing economies such as India, China, Bangladesh, Mexico and those in Sub-Saharan Africa.

According to the WHO and UNICEF, 844 million people on the planet, one in nine, do not have clean water close to their homes, leading to health issues through inadequate hydration, poor sanitation and personal hygiene, as well as hunger and malnutrition due to crop failure and animal mortality.

As weather patterns across the globe alter in response to climate change, water scarcity is projected to increase in frequency and geographical extent, contributing to half of the countries of the world facing water insecurity issues and outright shortages by 2025. Clearly, any engineered solutions that can sustainably help mitigate the impact of water scarcity are crucial to the lives of billions of people both today and in the future.

By way of one possible solution, in London there is a desalination plant commissioned in 2012 that is capable of producing 150 million litres of water per day - enough for 400,000 households.  Fortunately though it is yet to be used, as, for the moment, existing water supplies continue to cope.  Desalination however always involves big centralised plants located close to areas of high population density. For example, in Israel, who are the global leaders in desalination, the world’s largest facility is currently being built to supply up to 624 million litres of clean water per day for about 1.5 million people located in the surrounding area. Despite the innovative advances made by Israeli engineers to improve the efficiency of the process, the technology is energy intensive and expensive to both build and run. To meet the needs of the rural poor what is required is local, small scale, more agile engineered interventions, that offer energy efficient, affordable ways to provide water for use in drinking, sanitation, hygiene and agriculture.

As well as large-scale state-of-the-art desalination plants, Israeli engineers have developed an efficient, cost-effective, smaller scale technology that can provide up to 6,000 litres of fresh drinking water every day from moisture present in humid air, benchmarked at 26.7C and 60% relative humidity. This is sufficient to supply a small sized rural community in a developing country, where typically water consumption is as low as 20 litres per day for the average person. The company these engineers work for, Water-Gen Ltd, has also made available a more lightweight mobile version for easy transport that can deliver up to 650 litres a day. Both machines do however require either grid electricity or diesel gen-set supplied power to operate. In a world where 1.2 billion, mostly rural based, people have no access to electricity the provision of off-grid solutions is essential. This is particularly important in the case of developing economies, where diesel gen-sets are an unsustainable solution due to high costs, unreliable fuel sourcing and fuel price volatility.

One such solution developed by engineers at US company SunToWater Technologies LLC, is a highly efficient, innovative, standalone solar powered dehumidifier unit capable of producing between 150-380 litres of water per day from air with a relative humidity as low as 14%.  In this off-grid commercialised application, during a ‘recharging’ phase, air is blown over a salty material which absorbs up to six times its weight in water. In the ‘discharge’ phase, this is then extracted through the use of solar sourced heat and a condenser loop. In another, much simpler back-to-basics approach, Peruvian entrepreneur Abel Cruz recently set up 60 ‘fog catchers’ in the Andes around Lima to deliver water to the poor for crop irrigation and washing. Each low-cost unit delivers 50-100 litres of water per day. They are composed of a nylon net to collect moisture droplets from the air and gutters and pipes to transport the water to a storage vessel for onward distribution to users. 

Engineers working for UK companies are also coming up with a range of similarly innovative ways to produce water for poor rural communities suffering water scarcity. One such company, Inviro Choice Ltd, is however going a step further and ingeniously combining water production with water waste prevention.

Many rural communities in the world that are subject to the detrimental impacts of water scarcity are dependent for their livelihoods on food production from smallholder farming, in which water plays an important part. However, the tragedy for these communities is that in many cases as much as 50% of the food they produce is lost postharvest due to spoilage, so much of this water is wasted unnecessarily. It has been estimated that about 25% of the water used in food production globally is associated with food produce that ends up as wastage. Reducing postharvest food loss is essential to helping prevent precious water resources being wasted.

Cooling perishable produce such as fruit and vegetables to an optimum temperature immediately upon harvest is crucial in ensuring that food entering the supply chain has the best chance of maintaining shelf life for as long as possible. This is particularly important in the case of tropical and sub-tropical produce where ambient temperatures are high and, for example, a one hour delay in removing field heat from produce harvested at about 35°C can lead to a one day reduction in shelf life.

Engineers working at the Liverpool-based SME, have developed a postharvest chiller which has integrated solar PV, solar thermal and energy storage to support full off-grid operation, but importantly have also redesigned the chilling process to enable abstraction of the water produced by the cooling cycle. Standard operation of the system results in the removal of up to 5% of the moisture contained in the food produce being cooled (moisture removal beyond this limit is detrimental to the integrity of the product) and by simply capturing this it is possible to effectively recycle a portion of the water used in growing the produce and make it available for other uses. A single small machine with a 1 ton produce capacity could deliver around 600 litres of clean water per day during ten hours of operation.

What is clear is that there are many engineered ways to respond to our growing water shortages. Dehumidifiers, food chillers, fog catchers and desalination are but four of them described here. There will no doubt be more as we strive to continue to be “improving the world through engineering”.  What will link them all for sure is that combined with efforts to reduce our demand for clean water, we will solve the problem one drop at a time.

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