A team of Massachusetts Institute of Technology researchers have discovered a low-cost, natural way to filter water using tree branches, which may lead to alternatives to high-tech and expensive water filtration systems.

By using a filter fashioned out of a pine branch or other type of sapwood, a person can filter out more than 99 percent of E. coli bacteria from water, the MIT team found. The wood filtration is made possible by the size of the pores in sapwood, which allows water to flow through while blocking most bacteria from getting through.

The wood filter, which can produce about 4 liters of drinking water a day, is promising because of its low cost and efficiency, particularly for people in rural communities where advanced water filtration systems may not be available, according to Rohit Karnik, an associate professor of mechanical engineering at MIT and co-author of the research, which is published in the journal PLOS One.

"Today's filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily," Karnik said. "The idea here is that we don't need to fabricate a membrane, because it's easily available. You can just take a piece of wood and make a filter out of it."

Other water filtration systems, such as chlorine-based purifiers and filtration membranes, can be expensive. And even purifying water by boiling it requires a lot of fuel to heat the water.

Sapwood, it turns out, is inexpensive and very effective at doing the same job as other water purifying methods. Part of this has to do with sapwood's natural ability to filter out particles bigger than 70 nanometers. Sapwood filters can likely filter most types of bacteria, but not viruses, which are much smaller.

Currently, designers are working on ways to make the system viable, as there are still hurdles to overcome, such as not allowing the wood to dry out so much that its filtration properties fail.

"There's huge variation between plants," Karnik said. "There could be much better plants out there that are suitable for this process. Ideally, a filter would be a thin slice of wood you could use for a few days, then throw it away and replace at almost no cost. It's orders of magnitude cheaper than the high-end membranes on the market today."