Water Filter

What does a water filter actually filter? Assume a brita or one if those 100 devices you connect to your kitchen snk.

If my water report says 2 ppm on calcium, would it still be 2 ppm after filtering. What things on my water report would be affected?

You will have to be a little more specific on which filter you are talking about.
But filters such as Brita, really are carbon filters. These filters remove mainly chlorine and chloramines from your water supply. Everything else should be the same after it has gone through the filter. I am not an expert on this, but to actually strip water of its solids, you need a reverse osmosis filter.

Depends on the filter. Some are nothing more than wound cord and they do nothing but remove particulate matter, sand, mud etc. They effect no change in the chemical composition of the water. Some contain granulated activated carbon. These will reduce chlorine and chloramine but will have no effect on dissolved ions. Still others, and the Brita is in this class, contain carbon and ion exchange resins. They remove chlorine and chloramine and dissolved ions. Then there are home water softeners, microfiltation systems, and RO units.

Brita type filters do pretty well to remove the chlorine and chloramine. This is enough to keep many home brewers happy.

I buy RO water, but it's convenient as in Phoenix there's "Water and Ice" stores every couple blocks.

I found out, it's a Pur water filtration system. Have to check the cartridge to see if its the 3 stage filter. What is interesting is that it says stage 1 is sediment, 2 chlorine, benzos, asbestos etc and 3 says its filtered over natural minerals for a crisp taste.

Sounds like its adding something?