What is filtering?

Let's find out by putting a cotton ball into the hole in the bottom of a plant pot. We'll put several inches of clean sand into the pot, and the cotton will act as a plug to keep the sand in the pot.

Now, we'll put muddy water on top of the sand--maybe a cupful or so. The pot will be sitting in a little bowl, and the water seeping through the sand, and through the cotton, will collect in the little bowl.

How does the water look? Let's look at some of the muddy water, and compare that with the water that seeped out of the bottom of the pot.

So what? What's the big deal about filtering muddy water through clean sand?

This is what: this is the way that filtering is done in nature. It rains onto the ground, and makes mud-puddles. The muddy water soaks into the ground, and as it goes deeper and deeper, the earth through which the water seeps acts as a filter. By the time the water gets to the water table or an aquifer (pronounced "AH-kwif-fer"), the yucky stuff has been filtered out of the water.

Of course, some kinds of yucky stuff can go right through the filter. Also, if the soil itself is polluted, like with garbage or chemicals, the water will be contaminated by the
filter.

What can we do about that? Let's each write a short essay about contamination and what to do about it.

What on earth is an aquifer?