Children of Terra

A new generation, for a better world.


Dirty water? Clean it up by building a water filter!

Posted on August 15, 2018 at 11:30 AM

Water is one of the most important things for life. More than seventy percent of our planet’s surface is covered in water and more than 55 percent of our bodies are made of water. We drink it, use it to clean ourselves, cook with it, travel on it, hunt in it, and so much more! But… what happens when we don’t have clean water to use? What if it has been polluted or poorly managed? What if a natural occurrence makes our water unusable? Even fresh spring water may not be entirely safe to drink. This is why we treat our water. The water that comes out of your tap has been physically and chemically treated to make it safe for us to consume!

Water purification usually consists of four main stages: Coagulation, sedimentation, filtration, and sanitation.

-In the coagulation stage, special chemicals are added to the water that help dirt and other impurities clump to the chemicals or to each other, also called coagulation. These larger, clumped together particles are called floc.

-During the sedimentation stage, the now-heavier floc sinks to the bottom of resting water.

-During the filtration process, the floc-free water is passed through different types and sizes of materials. Materials such as sand, gravel, and charcoal catch particles of various sizes in them as the water is passed through.

-In the final stage, sanitation, water is either chemically treated or temperature treated to kill off any remaining parasites or diseases in the water. Adding chlorine or boiling the water are two such methods of sanitation.

For today’s project, we will focus on the filtration stage.

Here’s what you’ll need:

-A clean, empty 2-litre bottle



-Activated charcoal

-Blotting paper or a coffee filter


-A rubber band

-Some dirty water

What to do:

Start by cutting off the top 1/3rd of the bottle. The top piece will be the filter chamber, and the bottom will be the catch chamber. Remove the cap, and place your blotting paper or coffee filter over the hole. Use your rubber band to hold the paper in place. Flip the bottle top over, and place it into the bottom of the bottle. The filter chamber should look like it’s funneling into the catch chamber.

Next, start adding layers of filter material to the funnel. Generally, you would want the finer materials closer to the bottom of the filter, and the larger materials on top. In our filter, we put large gravel on top to catch large debris. Smaller gravel underneath to catch smaller debris, then sand under that to catch even finer debris and particles. The carbon in the charcoal attracts other carbon-based impurities, which bond to the carbon and get left behind as the water passes through. Lastly, that blotting paper or coffee filter is there to catch yet even finer particles. We did alternating layers of charcoal and sand in the bottom, fine gravel, then large gravel at the top. You can experiment with a different order of layers and different depths of certain materials to see which may have the best result.

Finally, it’s time to filter the water! Simply pour your dirty water into the top of the filter chamber, and wait for it all to pass through. If your filter works, you should notice the water coming out much cleaner looking in the catch chamber. If not, perhaps try reconfiguring your filter, or passing the water through it again.

When your all done, be sure to break down your filter and recycle its components. Use your filtered water for some plants, recycle the bottle or use it for another project (such as this" target="_blank">self-watering planter), and either set the gravel aside for another project or return it to nature. While your breaking down the filter, be sure to take a few moments to examine the blotting paper or coffee filter to get a better idea of what kids of pollutants were in your water before filtering.

PLEASE NOTE: Filtration is only one step in making water safe for human consumption. The water you filter in this experiment is likely not safe to drink.

Project notes: This is a really fun and easy project. Try tying it into other lessons, such as survival science, water treatment, water pollution, waste management, etc. etc… One thing that should be noted about our filter is that we didn’t use activated carbon for it. Instead, in an effort to replicate more of a “survival” situation, we used pieces of charcoal from our fire pit. Also, as a rubber band wasn’t readily available, we used a hair tie instead.

Really, your components for this project don’t matter much aside from the filter materials. You can use a plastic cup with holes punched in the bottom rather than a plastic bottle, or piece of PVC piping, or whatever is available to you that you can place the filter materials in and pass water through. Get crafty, make it interesting, explore, and learn!


CJ @ Children of Terra-NEO

We love seeing how your projects turn out! Share your water filter with us here, or on Twitter" target="_blank">(@ChildrenOfTerra), Facebook" target="_blank">( or on our new Instagram" target="_blank">(@childrenofterra). Let us know how you made it, what improvements you’ve made, and what materials you used!

Resources:" target="_blank">USGS-How much of the earth is water?" target="_blank">USGS-Water and you" target="_blank">CDC-Water Treatment" target="_blank">Water Filter Fast-The benefits of using a charcoal filter


Categories: leafSTEM: Connecting Science, Tech, Engineering, and Math with the Environment, Eco-Fun Kids Corner, Upcycling and DIY

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