[my_pointy_head_is_sharp]

I haven't heard about stage 1, 2 and 3 water filters. Could you explain a bit more about it, or direct me to a website? Thanks.

Also, what's a whole house filter? I've never heard of that either. And a UV light filter?

You've introduced things that I've never heard about.

[norraad]

Simple, each stage removes smaller bits than the one before it so they all last longer and provide better volume & pressure overall.

For me,

stage 1= 20 micron whole house filter(available real cheap @ Lowes, Home Depot, etc.).

Stage 2 = Brita ( about 2.5 micron, plus charcoal for chlorine, etc.)

Stage 3 would be the uv , which I don't yet, but it's on the list

This is just an example, some folks put two of the whole house filters in the basement & have the first one 20 micron & the second one 5~10 micron.

That takes the load off the more expensive Brita filters.

It's a mix & match type of deal. dependig on you situation.