How Does a Water Filter Work? What's inside?

If you have always wondered what's inside those pitcher and faucet water filters. Well,

wonder no more. We have cut apart a used up PUR pitcher water filter to show you what

is inside - water was no longer flowing through it. Most of these filters have three stages

of filtering in them - two physical stages: first and third and a second stage, which

is an active carbon filtering stage wedged in between the two physical stages. The first

stage is just a crude sediment filter, designed to keep large particles out of the rest of

the filter. The third stage is a pleated accordion style filter that takes out the finer size

particles and is made similar to air filters you will find in most automobiles, furnaces

and older vacuum cleaners. The second stage is what does most of the work, with the carbon

absorbing many of the impurities and much of the contamination commonly found in water.

This second stage also contains little Styrofoam balls like this. These Styrofoam balls do

not seem to have any water filtering purpose, but they do slowly make their way down from

the second to the third filter stage along with filtered water. As we look at the third

stage of the filter, we see that it is generally in a very good shape. In fact it looks so

clean that if it was in your car, you wouldn't even think of replacing it. The first water

filter stage is not bad either. We are on a well here and our water is rich in iron,

which explains the discoloration. This house also has a whole house sediment filter, which

takes out all the particles down to 2 microns, so we don't expect to see much sediment collected

by this first stage pre-filtering and we don't. Looking at the active carbon media, you can't

really tell how much more capacity to take up impurities it has remaining, but it really

has not had that much water pass through it and the water that did go through it is from

a very deep, and clean source. So, I would venture to guess that it would be perfectly

fine for a very long time still. So what is causing all these filters to plug up and stop

filtering. To answer this question, let's take a closer look at the third stage pleated

filter. If you look close enough you will see that the inner layer of this pleated filter

is non-porous, except that it has little holes in it and all of these holes are now plugged

up with those little Styrofoam balls that we showed you earlier. So, as these little

balls come down from the second filtering stage down to the third, they get caught inside

the little holes and clog the pleated filter entirely. In other words, this filter is designed

to fail before it can ever reach, under normal circumstances, anywhere close to its full

filtering capacity. And this is how P&G and its competitors in the water filtration business

make sure that they can sell you more of the consumables than you really need and would

otherwise buy!