jor,
Hi. This is artlover's daughter, writing to assure you that filters on tap water DO NOT REMOVE ALL POTENTIALLY HARMFUL CONTAMINANTS, biological or otherwise. Boiling the water is an additional preventative step I have recommended in my household, although I am painfully aware that this additional treatment by no means solves the problem of contaminated water. Water can contain organic as well as inorganic compounds, many of which are only regulated at POTENTIALLY CARSONIGENIC LEVELS. Boiling water (which we then refrigerate) can help remove harmful chlorine residuals (nitrates and nitrites are a particular health concern), and the boiling treatment will kill many biological contaminants that can be harmful that may have survived initial treatments, or entered the water after treatment occurred. Unfortunately neither of these treatments properly addresses inorganic chemical contaminants such as lead, arsenic, mercury, barium, cadmium, and URANIUM (not to mention PAGES more) that commonly contaminate municipal waters.
While the (graduate level) course in water health I am taking primarily deals with US waters, I can also tell you that water contamination is by no means isolated to the states. Different countries have different biological agents of concern, and use different treatment techneques (when treatment is available). One major difference between US and European water treatment is that most counties in Europe do not use chlorine in their water. Chlorine is the major disinfectant we use in the states, and is very effective at killing many (but not all) biological pathogens- unfortunately it often leaves residual chemicals (such as nitrates and nitrites, which can cause cancer) in the water supply.
While water treatment and filtration methods have greatly improved over the centuries, never before this past century have we dumped so many inorganic materials into our water systems. Water treatment is a short term, partial solution to an ever compounding problem.
I am not overreacting or trying to cause panic in others, but we should all be aware of these FACTS and do what we can to protect ourselves and legislate changes. The best way we can protect ourselves and future generations is to make it clear to our governments that we will no longer compromise environmental (and human) health for short term economic gain.
I apologize for this short novel I have posted here, but I firmly believe that knowledge is power, and hope I have properly conveyed what a major health and environmental concern water contamination is. If you would like to visit our class web site for our class notes (and as I told my mother, there is some disturbing information from very reliable sources there) the URL is
http://courses.washington.edu/h2owaste/

Other good sites to visit are
http://www.cdc.gov/ncidod/index.htm
http://www.epa.gov/safewater/
http://www.epa.gov/waterscience/ http://www.doh.wa.gov/ehp/dw/
to name a few.
Again, no intention of spreading panic, just facts. Best wishes to all (maybe together we can help address and remedy such problems).

Actually millions of people in 3rd world countries sicken and die every year from drinking contaminated and bacteria-ridden water. It's a leading cause of death in 3rd world countries--hitting children the hardest, but also adults of all ages.