Just came across this neat bit of nature tech at MIT: a water filter made out of sapwood.
It actually makes a lot of sense, wonder why nobody else thought of it. It filters contaminants, bacteria, and anything over 20nm in size.
From the article, it looks like you need some sapwood (basically a living branch where sap flows), a tube, and some glue or seal making material. Strip off the bark, stick the sapwood into the tube, and seal around the edges. Pour water in one end, clean water comes out the other.
I’m going to have to try this out in a future follow up post.