New 'water lens' uses sunlight to sanitise dirty water

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A ‘water lens’ developed by researchers from the University at Buffalo, New York, could potentially help the 1.1 billion people in the developing world who do not have access to clean water. The water purification system is extremely simple, consisting of just wood and plastic sheeting, and could therefore provide a low-cost and easy-to-assemble solution for communities with no safe drinking water.  

The 'water lens' consists of a plastic sheet covered in water that concentrates sunlight, and a wooden frame to hold a small container of water. The water in the container is held in line with a focal point created by a concentrated ray of sunlight. Barring the weather, once assembled, the lens functions freely. Due to the sun’s movement, the container needs to be aligned throughout the day to stay within the focal point.

The device is capable of heating a litre of water to 130-150°F in just over an hour, destroying 99.9 per cent of bacteria and pathogens.

Deshawn Henry, a sophomore civil engineering major, who carried out the research, tested how altering the thickness of the plastic sheet and the volume of water over the sheet affected the efficiency of the lens. The device was tested with plastic sheets that were 0.7, one, and two millimetres thick, and water volumes of four, six, and eight litres.

The study found that adding more water to the lens improved efficiency, as larger areas of water transmitted more energy from sunlight. However, thicker plastic sheets consumed more energy from light, lowering the lens’ efficiency.

A plastic sheet that was too thin or excessive amounts of water could break the lens. It was concluded that the 0.7 millimetre sheet could efficiently heat the container while supporting eight litres of water, but any more and the sheet could potentially break.

‘The water lens could have a huge impact in developing countries,’ said Henry, who carried out the research under James Jensen, professor in the Department of Civil, Structural, and Environmental Engineering. ‘Millions of people die every year from diseases and pathogens found in unclean water, and they can’t help it because that’s all they have. Either they drink it or they die.’

Professor Jenson added:'Deshawn’s work would allow a family in sunny regions to treat drinking water without having to expend energy or rely on imported technologies.'

Henry will now concentrate on building a larger water lens that remains efficient. A family of five, for example, would need a lens at least three times the size of the device he has constructed, Henry explained, which was designed to heat one liter of water at a time.

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Further Information

University at Buffalo