Originally posted by: Modelworks
The easiest solution for this is to get a filter that installs inline to the faucets cold water connection. They are cheap and easy to install. Turn off the cold water supply under the sink. Attach the filter to the shut off valve. Connect the water line back to other side of filter. It is a 20 minute job and you don't have to have that thing on your faucet all the time.
http://www.filtersfast.com/Omn...ater-filter-system.asp
If you want to do it really cheaply you can purchase a whole house filter , put the connectors on it to adapt to your sink and use that. It is far cheaper than any other way and the filter will last for many months on a sink. You also can choose from a wider variety of filters to suit your needs.
Something like this:
http://www.filtersfast.com/Pen...067-Filter-Housing.asp
Then add the filters:
http://www.filtersfast.com/Pentek-NCP-10-filter.asp
Single carbon block filter is the most economical to filter for taste of extremely clean & soft city water. However, most city water quality isn't with out impurity, therefore it will shorten the lifespan of the filter (1-2 months between filter changes for standard 10? cartridge).
If your city water is clean with out pipe rupture no drinking waring periods then a 2 stage system is the way to go for taste, and the cost isn't much higher than single stage filter to be a concern (common 2 stage filters: 20-30/1-5 micron polyfiber, and 5 micron carbon).
IMHO, if you are mucking about under the sink then might as well put in an RO system, because removes pesticide, insecticide, herbicide, arsenic, and nitrates that isn't remove by active carbon filter that could potentially enter city water service. However, the cost is relatively higher than 2 or 3 stage cartridge filter systems, and it also waste some water to clean the RO membrane.