University of California, Berkeley scientists have said that ionized plasma can not only can sterilize water, but also make it anti-microbial for as long as a week after treatment.
Devices able to produce such plasmas are cheap, which means they could be life-savers in developing countries, disaster areas or on the battlefield where sterile water for medical use - whether delivering babies or major surgery - is in short supply and expensive to produce.
"We know plasmas will kill bacteria in water, but there are so many other possible applications, such as sterilizing medical instruments or enhancing wound healing," said chemical engineer David Graves, the Lam Research Distinguished Professor in Semiconductor Processing at UC Berkeley.
"We could come up with a device to use in the home or in remote areas to replace bleach or surgical antibiotics," he stated.
Graves and his UC Berkeley colleagues reported that water treated with plasma killed essentially all the E. coli bacteria dumped in within a few hours of treatment and still killed 99.9 percent of bacteria added after it sat for seven days.
Mutant strains of E. coli have caused outbreaks of intestinal upset and even death when they have contaminated meat, cheese and vegetables.
In the study, Graves and his UC Berkeley colleagues showed that plasmas generated by brief sparks in air next to a container of water turned the water about as acidic as vinegar and created a cocktail of highly reactive, ionised molecules - molecules that have lost one or more electrons and thus are eager to react with other molecules.
They identified the reactive molecules as hydrogen peroxide and various nitrates and nitrites, all well-known anti-microbial. Nitrates and nitrites have been used for millennia to cure meat, for example.
Graves was puzzled to see, however, that the water was still anti-microbial a week later, even though the peroxide and nitrite concentrations had dropped to nil.
This indicated that some other reactive chemical - perhaps a nitrate - remained in the water to kill microbes, he said.
The study has been published n the November issue of the Journal of Physics D: Applied Physics.