Tag Archives: water filter

Charlotte Water Distance Learning: Make Your Own Water Filter

Activity: Build your own water filter (using household items)

Age Range: Upper Elementary – Middle School

It almost seems like magic the way that we can take water from a lake and turn it into safe, high quality drinking water from your tap.

For this activity, you can create your own magic by using household items to create a filter that is very similar to the way water is filtered and treated at our water treatment plants. Substitutions for materials can be used as needed – the idea is to understand how each step of the filtration process plays a key role in making your water safe to drink. 

First, it is important to understand what those steps are in the process. Today we are going to filter water through this five step process:

  1. Coagulation – During this step, liquid aluminum sulfate (alum) is added to the untreated (raw) water. When alum is mixed with the water it causes tiny particles of dirt in the water to stick together (coagulate).
  2. Flocculation – After alum as been added to the water, the alum and water mixture is stirred, causing larger heavier particles to form, called floc.
  3. Sedimentation – Once the floc particles have formed, the water is moved to a sedimentation basin where the heavy particles settle to the bottom.
  4. Filtration – After the water leaves the sedimentation basin, it flows through a filter made of layers of sand and carbon to remove any remaining particles left in the water.
  5. Disinfection – In this final step, chlorine is added to kill any germs or contaminants, and it keeps the water disinfected while it is pumped through the pipes. A small amount of fluoride is also added to protect teeth. (we will not replicate this step in our activity to keep it simple). 

Materials Needed: 

  • Large clear container filled with tap water
  • Dirt, trash, debris, or leaves (anything to make your water dirty)
  • One empty and cleaned 2-liter plastic bottle
  • Scissors
  • Two tablespoons of alum (this item can be found at the grocery store in the spices section. It is commonly used for making pickles.)
  • Sand
  • Gravel
  • Activated Charcoal
  • Cotton balls
  • Paper Towels
  • Coffee filters
  • A notepad and pen (for taking notes of your observations)


  1. Make the water “dirty” by adding dirt, trash, or other debris. 
  2. Cut your 2 liter bottle in half. 
  3. Turn the top half of the bottle upside down and place in the bottom part of the bottle. The top half will be your filter and the bottom part will collect your filtered water. 
  4. Using your materials like paper towels, coffee filter, sand, gravel, charocal, and cotton balls create your own filter system in the top half of the overturned bottle.  
  5. Look at the dirty water and describe what you see; take notes of what you see.
  6. Add two tablespoons of alum to the dirty water. This step in the process is coagulation. Take notes on what you observe during this process. You should begin to notice the dirt particles sticking together.
  7. Then, stir the mixture slowly for five minutes. This step in the process is flocculation. Write down a prediction of what you think will happen next. You should notice larger particles starting to form.
  8. Next, let the water to sit for 20 minutes; observe the water every few minutes and note and changes. This step is the sedimentation process. You should see the particles settling at the bottom of the container.
  9. After your 20 minutes is up and the large particles have settled, carefully pour the water through the filter. This is the filtration process. Take notes on what the water looks like after it passes through the filter.

How did your filter work? Did any adjustments need to be made to your filter? Write down any final observations and thoughts you have about this experiment.

As always, we would love to see your homemade water filters. Let us know how it went by tagging us on social media!