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Splish Splash: Make Your Own Water Filter

Splish Splash: Make Your Own Water Filter

Design and build your own water filter using common household items. Then watch as your water is cleaned before your eyes.

Pet Power

Part of our Outdoor Science Adventures
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What I'll Learn

Water is naturally cleaned through percolation (or filtration), but we can also filter water so it’s safer for us (and our pets) to drink.

What to Do

What I Need

What to Do: Step-by-Step Instructions


In order to clean dirty water in this experiment, you first need to create your own “contaminated water”. Fill one of your cups about half-way with tap water. Then mix in a little “contaminate” of your choice: you can use soil (or dirt), a colored powder drink mix, 1-2 drops of food coloring, or a splash of any water-based colored liquid found in your kitchen (such as soy sauce or red wine vinegar). To see how well you can remove large contaminates from your water, you can also mix in a few small materials, such as beads or rice. Set aside your contaminated water for now; you’ll use it again after you make your water filter.

Tips & Tricks:

You don’t need a lot of contaminates to make your water dirty. Even just a pinch of soil will do the trick.

It’s time to make your water filter. Have an adult help you cut the bottle in half horizontally across the middle. You will use the top half of the bottle as a funnel and the bottom half as a cup. To make this work, place the neck of the bottle upside down into the bottom “cup”.

Fun Fact:

It’s important your pet stays hydrated, especially when it’s hot. Just like humans, pets need clean and fresh water to drink, which means it’s not safe for animals to drink from puddles, ponds, the gutter, or any place where there is “standing” water. This water can carry contaminates that might make your pet sick.

To help keep your filtering materials from making their way into your clean water, place a coffee filter or paper towel inside the neck of the bottle, making sure it completely covers the funnel opening.

Fun Fact:

A coffee filter or paper towel will add an extra layer of filtration, helping to collect any large debris, and even some small contaminates, that have made it through the rest of your filtering system.

What materials do you think will work best to capture the contaminates in your water sample? You can layer several filtering materials, such as cotton balls, cheesecloth, sand, gravel, and activated carbon. Spread your first layer of filtering material on top of the paper towel or coffee filter, making sure none of it falls into your lower “cup”. Then layer other filtering materials on top. How much should you use? That’s up to you! Generally speaking, more filtering material means more opportunities for your contaminated water to be cleaned.

Fun Fact:

Activated carbon is oven-dried burnt wood that captures and clings onto tiny contaminates, such as food coloring. But it doesn’t work forever. When the surface of activated carbon is completely covered, it cannot grab any more contaminates, so they will pass right through. This is why it’s important to replace the activated carbon filter in your fish tank about once a month.

Now it’s time to test your water filter. Larger items in your contaminated water may have settled onto the bottom of your cup. That’s great, actually! Gravity has already started to help you clean your dirty water. Pour about ¼ of your water into your second clear cup. Then set this cup aside. You will use this as your control to see how well your water filter worked.


Slowly pour the rest of your contaminated water onto the top of the water filter, letting the water make its way through the layers. If your water begins to collect on top of your layers, give it time to percolate (filter) through your layers before you add more.

Fun Fact:

Water molecules are small and can move through tiny spaces in sand, rocks, and soil. At the same time, these tiny spaces can capture contaminates, helping to clean your water. Natural spring water is cleaned using only earth-based materials. But don’t let bottled water companies fool you. They collect their “natural spring water” and pass it through additional filters to make sure it is clean for you to drink.

Once the contaminated water has drained into the bottom “cup” of your bottle, compare it to your un-filtered control water. Does it look like it has cleared up? If so, your filter is working! If not, does it look cloudy? Never fear – this just means some of the tiny particles of your filtering materials (such as dirt clinging to your sand or rocks) has also made its way through your filter. These should get captured by your water filter system if you pass it through again. In fact, the more you pour your contaminated water through the filter, the cleaner it should get. Make sure you compare it to your control each time it gets filtered.

Now that you have learned how water is naturally cleaned and tested some materials humans use to purify water, make sure you always have fresh, clean water for your pet to drink. If your pet lives both inside and outside, make sure you have a fresh bowl of water in both places, replacing it at least once a day or whenever it starts to look dirty. If you have a fish, make sure you regularly clean the tank and replace the filter. This will help your pet stay hydrated and healthy.