Scientists at Stellenbosch University have used a tea bag, traditionally used to infuse water with flavour, to do the opposite by purifying water.
The tea sachets are designed to suck up toxic contamination when fitted into the neck of a water bottle.
The researchers, at Stellenbosch University, South Africa, hope communities that have no water-cleaning facilities will use it to purify dirty water.
The sachets are made from the same material used to produce the rooibos tea bags that are popular in South Africa. But inside are ultra-thin nanoscale fibres, which filter out contaminants, plus active carbon granules, which kill bacteria.
"What is new about this idea is the combination of inexpensive raw materials, namely activated carbon and antimicrobial nanofibres, in point-of-use water filter systems," Marelize Botes, researcher in the university's department of microbiology, told SciDev.Net.
A sachet can clean one litre of the most polluted water. Once used, it is thrown away and a new one is inserted into the bottle neck.
Although the filter is still in development, tests on river samples around Stellenbosch have been successful, said Botes.
"The nanofibres will disintegrate in liquids after a few days and will have no environmental impact. The raw materials of the tea-bag filter are not toxic to humans," she added. Each bag should cost around three South African cents.
"Anybody can use it anywhere; it's affordable, clean and environmentally friendly," said Jo Burgess, manager of South Africa's Water Research Commission.
The inventor, Eugene Cloete, dean of the faculty of science at Stellenbosch University and chair of Stellenbosch University's Water Institute, which opened in June, said: "This is a decentralised, point-of-use technology".
The filter is expected to be on the market before the end of the year if approved by the South African Bureau of Standards, which is currently testing it, said Botes.