Pitcher and faucet-mounted filters generally rely solely on activated carbon filtration. While activated carbon is very effective at removing a wide range of contaminants, the problem with this type of filters is that they contain a very small amount of activated carbon. Further, the time the water spends in contact with the carbon, particularly with faucet mounted units is too little to provide full absorption. The removal rates for faucet mounted and pitcher style units is generally 30-60%.
Yes and no. A rolling boil for a least two minutes is effective in killing harmful organisms such as e.coli, giardia and cryptosporidium. However, boiling does not remove many other contaminants such as heavy metals, in fact, it concentrates them. While these contaminants do not often cause immediate acute sickness, long-term exposure to them is certainly unhealthy, especially at concentrated levels.
Not necessarily. To become certified by NSF, water filter manufacturers have to pay NSF various fees on an ongoing basis. A large number of manufacturers choose not to pay these fees and therefore not to have their products endorsed by NSF. Many of these manufacturers produce filters that are more effective than those produced by companies that have opted for NSF certification. You should evaluate a water filter based on the materials it is composed of and the reputation of the company that stands behind it.