04/05/2015 9:49 AM IST | Updated 15/07/2016 8:25 AM IST

Sari, Sunlight Is All You Need To Make This Low-Cost Water Purifier

SAM PANTHAKY via Getty Images
Indian women carry drinking water utensils at Tilakwada village near Sardar Sarovar Narmada Dam on Narmada river at Kevadia Colony, some 175 kms from Ahmedabad on August 29, 2011. The dam is one of India's most controversial dam projects and its environmental impact and net costs and benefits are widely debated. AFP PHOTO / Sam PANTHAKY (Photo credit should read SAM PANTHAKY/AFP/Getty Images)

BENGALURU -- A discarded sari, a few glass pipes, and freely available sunlight are the only requirements for an innovative system that can provide safe drinking water to a rural household.

The unique low-cost solar water purifier (SWP) does not require electricity and can be produced by village craftsmen, claim its developers at the Nimbkar Agricultural Research Institute (NARI), an NGO working at Phaltan in rural Maharashtra.

Also, unlike commercially available water purifiers, the SWP does not suffer from problems like filter clogging or wastage of water, NARI director Anil Rajvanshi told IANS.

Boiling the water is a recommended method to kill any disease-causing bacteria that may be present. But to boil the water, one requires electricity or other fuel.

NARI's purification strategy exploits the fact that boiling the water to make it germ-free isn't necessary. Low temperatures are sufficient for sterilising water provided the temperatures are maintained for an adequate time.

"Our earlier studies have shown that water heated to only 50 degrees Celsius and maintained at that temperature for one hour, or heated to 45 degrees and maintained for three hours, becomes completely free of coliform bacteria," Rajvanshi said.

"The presence of coliform is an indication that pathogens (disease causing germs) are present. The bacterial colony count was done in the institute's microbiology lab according to international protocols," he said.

A simple strategy for sterilisation, he said, is to filter the water (drawn from a well or a stream) to remove particulate matter, raise the temperature to about 45 degrees, and maintain that for at least three hours, he said.

This was accomplished by NARI in a cost-effective way in two steps.

For the filter, Rajvanshi's team used a piece of cotton cloth (typically from a sari) folded four times. According to NARI's earlier research published in the journal 'Current Science,' the four-layered cotton cloth acts as an excellent water filter.

Then, the team used solar energy to sterilise filtered water.

In essence, NARI's purifier system consists of four slanting tubular solar water heaters attached to a manifold with a receptacle at the top to receive the sari-filtered water. The water entering the tubes, each with a three-litre capacity, get heated by sunlight. "The tubes, made of toughened glass are basically long thermos flasks," Rajvanshi explained. "Once the water gets hot, the tubes maintain the temperature long enough to sterilize it."

"Tests done by NARI on this water purifier for the last one year have shown that even on a completely cloudy and rainy day, water is heated to high-enough temperatures to make it potable," Rajvanshi said.

Thus a simple solar water purifier for a rural household can deliver 15 litres of drinking water daily, he said.

The cotton cloth is the only consumable in the whole system, said Rajvanshi. "We have tried to use the cloth from the cheapest cotton sari available locally. It is washed every day after filtration and is holding good for the last one year. After a couple of years the sari will wear out and so it has to be replaced."

According to Rajvanshi, the system costs Rs. 1,500. "NARI has not patented this technology since it feels that it should be made available freely for the rural population," he said, adding, "Any small rural workshop can fabricate it."

For the last one year, two such systems at NARI are producing around 30 litres of potable water for all its staff members, Rajvanshi said.

NARI is now exploring the possibility of scaling up this technology for village level application so that 30,000-40,000 litres of potable water can be delivered."

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