Bacteria are present everywhere in our environment. They can live and reproduce inside animals, humans, in water, soil, and food. Most bacteria in small numbers do not cause health problems, but bacteria that enter the drinking water system at weak spots or breaks in the plumbing can grow to large numbers in the pipes when water is not used for long periods of time (like during long weekends or summer breaks). Bacteria’s ability to grow to large numbers in the system is usually slowed or stopped by the continued use of water, flushing them out.