Bacteria have been shown to live in "premises plumbing systems". The latter refers to the "pipes and fixtures within a building that transport water to taps after it is delivered by the utility". Community water systems have been known for centuries to spread waterborne diseases like typhoid and cholera. However, "opportunistic premises plumbing pathogens" have been recognized only more recently: Legionella pneumophila, discovered in 1976, Mycobacterium avium, and Pseudomonas aeruginosa are the most commonly tracked bacteria, which people with depressed immunity can inhale or ingest and may become infected with. Some of the locations where these opportunistic pathogens can grow include faucets, shower heads, water heaters and along pipe walls. Reasons that favor their growth are "high surface-to-volume ratio, intermittent stagnation, low disinfectant residual, and warming cycles". A high surface-to-volume ratio, i.e. a relatively large surface area allows the bacteria to form a biofilm, which protects them from disinfection.
Sometimes a faucet leak can be stopped by replacing the rubber washer at the end of a faucet stem or cartridge. This is a more common repair on older fixtures when things were built to last and designed to be able to be maintained. Other times the whole stem or cartridge needs replacement or the bibb seat deeper back into the fixture needs replacement. That leads to matching up the right components and often times making a trip to the hardware store or plumbing supply house necessary due to the many varieties, makes and models of faucets. My advice is to make sure your Plumber has faucet repair kit on their truck before having them come out to assess the issue.
Another way to avoid a service call from your plumber is to make sure the outside faucets are turned off in the winter and make sure you disconnect the outside hoses. You need to shut the water off from the inside. Then, open the valve on the outside to let the water that’s in there drain out—you switch both of them to the opposite direction so one is always closed and one is always open. We have to fix tons of these in the spring mostly because people leave their outside hoses connected and they freeze up. The repair could cost $100-$200 or more. Another tip would be if you’re going away for any length of time, like on vacation, turn off your water. If on any of those days the temperature drops below freezing, have someone check in on your house. I’ve been called to homes where the family returned from vacation, and there was water flooding out from the front door.