Are There Water Filters Growing in Your Backyard?
According to a March 2023 United Nations World Water Development Report, around 2 billion people do not have access to clean and safe drinking water. (Billions of people lack access to clean drinking water, U.N. report finds) Many organizations develop new water filters every year, but the major problems with these filters are the cost and availability: even relatively low-cost filters are prohibitively expensive for many. Also, people would rather pay small daily increments for fresh water rather than a single large payment for a filter. This is one reason that many people in India pay daily to have access to fresh bottled water, rather than purchase a filter that costs more.
Researchers at MIT found that local trees have natural filters that can actually purify water to drinking water standards. (MIT engineers make filters from tree branches to purify drinking water) Xylem is the vascular tissue that conveys water and dissolved minerals from the roots to the rest of the plant and also provides physical support. Xylem tissue consists of a variety of specialized, water-conducting cells known as tracheary elements. (Britannica.com) The interiors of non-flowering trees like pine and ginkgo have sapwood that contains xylem which even filters out bacteria. The sapwood of such trees also have shorter conduits in the xylem than flowering trees, so that water must pass through a number of “pores” in the xylem, which are the main filter elements that remove microbes. In trees, the pores are not used to filter water, but rather separate gas bubbles that would block the xylem. Here is a diagram of how water is filtered through xylem; the pores being the disc-shaped aperatures:
Courtesy: N.R. Fuller, Sayo Studio
Although the images above are microscopic, the entire filter is a 1-cm long piece cut from the cross-section of a branch:
Source: Xylem Water Filter manufacturing process video
Next, the wood filter is inserted into a tube and secured with a hose clamp. Voila, you have the main part of your wood water filter!
Source: Make your own Xylem Water Filter! video
Two additional preparation steps of soaking the wood filters in ethanol and drying them out completely in an oven caused them to be less prone to clogging, as well as extending their shelf life.
The researchers took the concept to a suburb in the Indian city of Delhi, where 30 million people live. Many people there are susceptible to intestinal illnesses and death due to poor quality drinking water. The MIT team went into neighborhoods with water access issues and demonstrated that the filters were simple and cheap to replace. Many people who saw them demonstrated confirmed that they could either make or purchase the wood filters sustainably, for easier access to clean water.
Want to make a xylem filter yourself? This free website gives all the information needed to select a tree and construct the filter, which is a great science experiment for kids.
The filters are still under development, because it’s not known whether they can remove chemicals, metals or other contaminants. However, unlike many novel water filters coming from universities or private firms, this one is quite inexpensive, simple and has easily-sourced parts. It seems that even survivalists should be glad to know this information–and you might want to keep it handy for your next camping trip!