Pure water at low cost

New simple and cheap processes to disinfect drinking water offer business opportunities in areas where potable water is not available.
Many of the poorest people of the world lack piped water and connected energy, and there is frequently an unfulfilled demand for safe drinking water. Without safe drinking water, huge problems arise with waterborne diseases and diarrhoea. UNICEF (the United Nations Children’s Fund) says "every day 5,000 children die worldwide as a result of diarrhoea caused by drinking unsafe water".
Water purification technology is widely used in developed countries and urban areas. However, its high cost, energy demand and complex operation make it unsuitable for small poor rural communities.
Two approaches which overcome these constraints have received attention recently: solar disinfection and solar distillation.
Both of these can be set up to run on very low-cost, locally-built equipment. Both require neither energy nor chemical inputs.
For business people, they offer the opportunity of supplying equipment and building/installing equipment for selling safe drinking water, and as pure and almost-sterile distilled water.
Solar disinfection
Just as UV disinfection sterilizes process water in the food processing industry, the UV-A radiation in sunlight destroys dangerous pathogens, making water safe to drink. At the same time the water is heated by the sun, increasing the radiation effect, especially when the temperature exceeds 45°C.
The basic equipment is simple. Filling an unused plastic bottle and placing it on the roof of a house in the tropics, yields sterilized water within six hours on a day of up to 50% cloud cover.
Now, this method has been formalised and developed into a system that includes operation manuals and training material.
More complicated setups connect a large number of bottles together and mechanise the filling and emptying of the bottles. Other systems could be developed – all that is essential is that the water is exposed to sufficient solar radiation.
If clean and disinfected drums were used it would be possible to set up a business selling this water – and drinks made with this water.
Various commercial devices have been designed, but they tend to be expensive and not really suited to be the basis for businesses.
There are constraints: in a rainy period, disinfection is not possible; also, the water needs to be clear to allow the sun’s radiation to pass through it.
It must also be realised that disinfection doesn’t alter the chemical composition of the water and does nothing to reduce water shortages.
Solar distillation
Disinfection of water can also be achieved by distilling water. Although solar distillation has been used for many years, now a simple and innovative device, the Watercone, is set to make this process more accessible.
The Watercone is simple to use: the transparent plastic cone is placed over any water. Solar energy evaporates the water under the cone, the vapour rises, condenses on the sides of the cone and trickles down to a trough around the base from where it can be collected.
This is probably a more practical ongoing solution than solar disinfection since it can be used with dirty water and it is fail-safe because whatever water is collected is guaranteed to have been disinfected (because it has been distilled). The cone costs $30.
Again here, however, there is a major constraint, namely that the Watercone can produce only 1.5 litres per 24 hours.
However, the principle can be applied using locally-available materials such as plastic sheeting and devising different ways of condensing and collecting the evaporated water.
Besides the sale of safe drinking water (and drinks made with the water), there is the potential to sell distilled water for other uses (such as battery water, medical uses and cases where water needs to be free of dissolved and undissolved material).
The process can also desalinate sea or brakish water. – Dave Harcourt
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