Is filtration enough to ensure that the water from the faucet is cleaned and purified? How much filtration should be done to ensure that the water is purified?
Assuming that you are filtering municipal water which has been treated, a good carbon block <a href="http://www.healthybizhealthyhome.com/countertopwaterfilters.html">countertop water filter</a> will remove chlorine, bad taste and odors, and some of the larger biologicals. Since most city water is treated with chlorine, you shouldn't have a problem with biologicals. If you are in a rural area drinking untreated well water, I would consider reverse osmosis.