DIY Water Filter

I walked into class at our flagship Lab in Wyoming one afternoon and posed the following question to the class. “If we were camping and forgot to load the cooler with water and we didn’t have a filter what would we do?”

Of course, with a class of 3rd and 4th graders, I got answers like “I’d drive back to town” to which I replied, “But the battery also died because you left the dome light on.”

“Well, I’d just drink Mountain Dew!” which I shot down with “…and we forgot all the sodas and fruit juices.”  As you can imagine, this volley continued for ten minutes until they relented and accepted their hypothetical fate.

Eventually, a voice from the crowd suggested we build a filter.  Eureka!

With our mission firmly establishes we set out to determine what natural inputs we might have to work with on our camping fantasy.  Below is the outlined process for creating a dirty water sample that might resemble something we would find in the backcountry and supplies for building the filter using items that were available at the Boys & Girls Club.

Disclaimer: As a nerd, I already knew I wanted a vessel for the filter that would hold up to repeated use so I cut the bottom off of a wine bottle.  As you might assume, that is not a product that is readily available at the Boys and Girls Club!

Build a Water Sample

What might you find in a backcountry water supply like a stream, lake, or pond?  Pine needles, leaves, dirt, rocks.  All found their way into our sample.  The task I presented to the students was to scour the yard for items that would be present in the backcountry of the Bighorn Mountains.  They all spend time in the mountains we call home so it took just minutes for them to create a nasty water sample to test the true grit of our filter.

Key: Try to include inputs that range is size so that the filter can be deconstructed and each layer can reveal what it filtered out.

Gather Components

Next, the students were asked to find three things: a container for the filtered water, sand and pebbles for the filter media, and some sort of filter membrane to plug the end of the filter and hold the other media in place.

The results were impressive.  They sourced sand from a poorly constructed raised planter built years earlier.  The soil mix was heavy on sand which had settled to the low corner of the tilted box.  The pebbles were found at the edge of the parking area, and the cotton swabs were “borrowed” from the medical room.  Several students had used these swabs to stop a nose bleed.  They swell as they absorb making them a very solid option for the neck of the bottle.

Note: I provided activated carbon from our backyard firepit.  We discussed where we might find it on property and were not able to identify any viable sources.  Of course, the boys in the group were anxious to burn something to make it themselves.  Though I never confirmed, I’m almost certain that such an activity would NOT be covered by our insurance policy!

The Cotton Filter

The first step we took in the construction phase was to insert five cotton swabs into the neck of the bottle.  This would serve two purposes: hold the other media in and provide a fine filter media as they water dripped into the collection container.

These swabs are used for major cuts and bloody noses.  We’ve found several uses for them in the Edible Learning Lab!

Note: During our first run at this filter we used five swabs.  In subsequent builds we used just four which allowed the water to flow at a slightly higher rate.

The Media

The final step in the build was loading the three media types into the bottle.  The charcoal goes in first and is held in the bottle by the swabs.  Charcoal filters out bacteria and some chemicals that might be present.  Charcoal is followed by sand which filters out smaller particulates, many not visible to the human eye.  The final layer is a few inches of pebbles that grab the larger debris like leaves, pine needles, or creepy crawlies.

The completed DIY Water Filter

The entire build takes about 15 minutes to complete, describing each step as you go.  It’s an impressive end product and the students will be itching to give it a try.  So get to it!

Filter Sample and Test

The video shows our first test.  As you see, it works like a charm but the reality hits hard when they realize how long it would take to filter enough water for everyone to enjoy a glass.

So we took our conversation a step further.  What would it take to scale up our filter?  What equipment could we use to build a larger version?  They students had some good ideas but that’s for another post!

I continued to filter water for the remainder of the day and we then deconstructed the filter the next day.  The large debris caught by the pebbles was easy to see.  The sand was discolored in a few areas suggesting that it had sequestered something.  The charcoal didn’t show any visible signs which makes sense given that bacteria and chemicals are not visible to the naked eye.  And the cotton swabs had darkened slightly proving that they did their job.

This classroom project is perfect for any class exploring water, filtration, design, engineering, chemistry, or a host of other STEM concepts.