Gather Materials

• Besides a two-liter bottle, you will need several filtering ingredients and a spout for your homemade filter. Get either granulated activated charcoal or carbon in either block or powder form. One of these ingredients will serve as the main component of your filtering system. When water passes through charcoal or carbon, lead and other unhealthy particles and contaminants, like fluoride and chlorine, are removed, allowing pure, unpolluted water to pass through. Carbon is thought to be more effective at removing contaminants than charcoal.
  
  You will also need fine and large-grained sand, fine and large-grained gravel, cotton batting and a coffee filter for the actual filtering, a straw for the spout, and some standard supplies, such as a utility knife and soap and water, to complete the project.
  
  

Making the System

• Begin your filter by cutting the bottom off the two-liter bottle with a utility knife. Try to make the cut as straight as possible, but it need not be perfect to work effectively. Once the bottom is removed, wash the bottle out with soap and rinse thoroughly. Cut a hole in the cap of the bottle that is just large enough for a straw to pass through. Cut a two-inch piece of the straw to serve as your spout. Push the straw through the hole in the cap so that it is halfway submerged in the bottle. The straw should fit tightly in the space. If it doesn't, wrap the straw with tape to make it a tight fit. Line the bottom of the bottle with cotton batting and place a layer of charcoal or carbon on top of the cotton. Layer fine grain sand and then large grain sand over the charcoal or carbon, then fine gravel and large gravel on top of that. Continue to layer these items in the same order until the layers reach the top of the bottle. Top the layers with a coffee filter.
  
  

Using the System

• Place the end of the bottle with the spout into a container. Pour water through the coffee filter. It will run through all the layers. Sediment will catch in the cotton batting, and pure water will flow out the straw spout.