Filter Water with Dirt

The Seasons

(Earth Science for ages 5+)

Have you ever filled up your water bottle from a freshwater stream or lake? Did you notice that the water is not very clean looking?

Most of the water humans drink come from surface water (streams, rivers, lakes) or groundwater (underground aquifers that store freshwater), but before we drink it, the water goes through several filtration and cleaning processes to make it safe and drinkable.

Maybe your parents have a water filter connected to the faucet or in a pitcher that you can use for drinking, but how do these filters work exactly? And did you know that water is naturally filtered through the ground in nature? The video above shows us how to recreate this natural filtration right at home. Here’s how you can do it, too:


2-liter plastic bottle (cut in half with the help of an adult)
Large bowl or jar
Dirt (potting soil works well)
Cotton balls
Gravel or small rocks
Adult supervision (Adult supervision at all times please)


  1. Start by making some dirty water. Using your large bowl or jar, add water and then mix in some of the dirt or potting soil.
  2. Next, create your water filter by first setting the top half of the 2-liter bottle upside down inside the bottom half (see the video for a visual aid).
  3. Take a handful or so of cotton balls and stuff them into the top half of the bottle. Next, layer some sand on top of the cotton balls, and then layer the gravel or small rocks on top of the sand. Now your water filter is ready to test.
  4. Pour the dirty water you made in step 1 into your water filter. Pour it slowly so it doesn’t overflow. The filter may take some time to process the dirty water so just be patient. What do you notice about the water that filters into the bottom half of the bottle? Is it cleaner than the water you poured into the filter? You might notice that the “clean” water still looks a bit dirty. This clean water is probably not clean enough to drink, but it can be reused for watering your plants.


When it rains or when the snow melts, water works its way into the earth and filters through before making its way to a stream, river or lake. First, it filters through gravel or rocks where big particles are captured, then it works its way through sand where smaller particles are captured and filtered out.

Finally, water slowly filters through clay or similar substrate that captured most of the small dirt particles. Water filters that are used in the home work similarly in that they have many layers meant to catch different sized dirt particles or contaminants before you drink it.