Filtration Definition: Lesson for Kids

Instructor: Elizabeth Hance

Elizabeth has taught elementary and middle school special education, and has a master's degree in reading education.

In this lesson, you'll learn about a process called filtration. You'll explore types of filtration, find out about ways to remove solids from a liquid, and learn to make your own filter.

What is Filtration?

Filtration happens every day around the world to get a liquid that everyone needs: clean water. Imagine going to a stream or lake and scooping up a bottle full of water. Chances are, the water inside won't look like the water that comes out of your faucet! It may be discolored, and you'll probably see some dirt and other debris floating in it. What you might not guess is that you can make that water clean by filtering it.

This basic filtration diagram shows the feed, filter, and filtrate.
filtration diagram

Any filtration system has a few basic components: the feed, the filter, and the filtrate. The feed is the original fluid. In our example of stream water, it's the water you scooped out of the stream or lake. The filter is the mechanism through which you pour the feed. The fluid that comes through the filter is the filtrate, or in our case, the water that you would want to drink.

Types of Filtration

Many types of basic filtration happen in your kitchen. If you make coffee by pouring hot water over grounds and letting the liquid pass through a coffee filter, you are using filtration. The filtrate is the coffee you drink, and the filter keeps the solid coffee grounds from ending up in your cup of joe! Want some fresh squeezed orange juice? You'll need to use a basic filter to keep the seeds and most of the pulp out of your juice.

Using a coffee filter is a common example of filtration.
coffee filter

Hot or cold filtration involves heating or cooling solutions to remove solids or other particles. These types of filtration generally take place in a laboratory when a scientist wants to remove impurities from a solution.

There are two main types of filters. The first is a surface filter or sieve, which is generally shaped like a cone and sometimes used with a paper filter. This is the type of filter you would use when making coffee. A surface filter allows you to collect particles or impurities that don't make it through the filter.

Water filtration takes place using a depth filter.
water filtration

The second type of filter is a depth filter, and it might seem a little bit backwards. A depth filter is made of a granular material, like sand, which collects solid particles as a liquid is poured over it. Unlike a surface filter, the impurities or particles will be collected throughout the filter. It seems strange, but you could pour water through sand and gravel to make it cleaner!

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