Add this one to your survival books, or, more impactful, to current water-filtering technologies around the world: A team of researchers from M.I.T. demonstrated how a stripped branch from a pine tree -- a sapwood -- can act as an improvised water filter by sifting 99 percent of E. coli bacteria from lake or river water, the school's website reported. They published their findings in the journal Plos One.

The process works by fastening a tube (or someting of that nature) at the end of the stripped sapwood and dripping water slowly through its exposed end.  

M.I.T.'s system trades off the natural processes of plants. Below the sapwood's hard exterior is softer, porous tissue known as xylem that's responsible for weeding out life-threatening bubbles while maintaining the easy flow of sap. It can filter particles as small as 20 nanometers (the smallest bacteria is 200 nm). It can't, however, keep out viruses and salt (so don't try it with ocean water). 

"Plants have had to figure out how to filter out bubbles but allow easy flow of sap," co-author Rohit Karnik, an associate professor of mechanical engineering at MIT, told MIT.edu. "It's the same problem with water filtration where we want to filter out microbes but maintain a high flow rate. So it's a nice coincidence that the problems are similar."

Karnik and colleagues tested the branches' abilities using water mixed with red dye. Most of the dye stuck to the branch while the water trickled into the collecting tool below. They repeated the experiment with E. coli infested water, establishing the filter's 99 percent blockage rate of the bacteria that can lead to serious infections.

Even if sapwood can't keep out everything, Karnik sees his team's discovery, if refined, as a cheaper and more accessible solution than current filtration methods.

"Today's filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily," Karnik says. "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."

As is, the tree branch could be used in parts of the world where people collect surface water polluted by microscopic dust particles and decaying plant and animal matter, according to the report.

Karnik and colleagues will next test the filtration properties of other types of plants.

 "There's huge variation between plants," he 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."