Rinse out a plastic bottle or jug so that it is clean on the inside.
Cut off the bottom of the jug or bottle. This is so that you can easily fill it with water for filtering. Rinse the container and dry it with a clean cloth to remove any residue resulting from the cutting.
Puncture the lid of the bottle or jug with a utility knife to create a hole that you can easily slide a drinking straw into. The hole must be big enough so that the straw does not bend when it is inserted, but not so big that water can flow out around the straw.
Make a spout out of the drinking straw by cutting off a piece of it with the utility knife. The size of the piece you cut depends on the size of your bottle or jug. It should be long enough to fit through the hole of the lid and protrude on both sides. Two to 4 inches is generally a good size. Once you have the piece, slide it into place in the hole. Secure it with waterproof tape if it doesn't fit snugly in the hole.
Hold the jug or bottle so that the lid is at the bottom and the open bottom is now at the top.
Add a layer of cotton batting to the bottle or jug. On top of that, add a 1/2--inch layer of carbon or charcoal powder. Then add a 1/2-inch layer of fine sand. Over that, add a 1/2-inch layer of large-grain sand, then a 1/2-inch layer of fine gravel and then 1 to 2 inches of large gravel.
Repeat the layers, in order, until you reach the open top of the jug or bottle. Cover with a coffee filter.
Position the drinking straw spout over a clean cup or container and pour water into the filter you made. As the water flows through the layers of filtration, iron and other impurities are removed before the water flows out of the drinking straw spout and into your cup.