Ever notice a cloudy film starting to build up inside your water pitcher? I had read that it was harmless, and since my pitcher held filtered water, I followed directions and didn't worry about it, cleaning the pitcher and changing the carbon filter every few months.
For years I've depended on my filter pitcher to improve the taste and smell of our water. And when I noticed a biofilm that kept coming back, I actually tossed out the whole pitcher and starting using a new one, just in case. The new one looked cleaner for a short time. But a recurrent health problem finally drew me to do a little research on filtered water. The growth in my pitcher is most likely pseudomonas aeruginosa. To avoid boring you with a long treatise, I'll just type in a few comments and provide links so you can read as much as you like.
Our local water company does not test specifically for pseudomonas bacteria. The director wrote that "
pseudomonas occurs naturally and can introduce itself to palnts, animals, soil, and water. If you are noticing any growth in water pitchers and damp surfaces, routine disinfection is recommended." He sent me an informative link about
Pseudomonas aeruginosa infection: http://emedicine.medscape.com/article/226748-overview. That article continues on multiple pages so you can read as much as you want. But what you need to know is that this bacteria does not usually cause serious problems unless you ALREADY have a health problem OR are elderly or hospitalized, but it CAN cause pneumonia, urinary tract infections (UTIs), bacteremia, and numerous other conditions, some of which are life threatening.
Activated carbon filters remove organic contaminants including chlorine from water... but they "can be a breeding ground for microorganisms. The organic chemicals that are adsorbed to the AC [activated carbon] are a source of food for various types of bacteria."
My reluctant conclusion is that pour-through filters are not a good solution to water quality problems. And damp areas around the sink and so forth need to be disinfected and dried frequently.