I forget sometimes that I am privileged with my tap water, and it is not only perfectly safe to drink, but I actually like the taste (generic hard water), I dont like soft water.
Most of the people I know around here that have a water filter primarily use it to filter out the limescale before pouring the water into the kettle.
As a question on a slightly different tangent, why do you want/need a filter, you say that the water is not up to standard, is that a health standard, a taste standard, both, or something else.
Main PC, P180, CM Silent Pro 500M, Phenom 840 @ 3.6GHz, 8-GB @ 1,866MHz, 256 GB Samsung 830, 500-GB 7K500, MSI 660Ti Twin Frozr, PC is quieter than my monitor :o
Server, 6-TB RAID-5 array, + 2 x 2-TB backup drives, 380W Enermax Pro82+, 4x very quiet fans, positive pressure only, no exhaust fans
Living Room PC, 3500+, 2-GB RAM, HD501LJ