Microbial biofilms are found anywhere that moisture and a suitable solid surface for bacterial attachment exist.
Dental plaque is one of the best known examples of a biofilm.
Microorganisms found in dental unit water are, in general, normal inhabitants of the public water supply including bacteria and some protozoa and fungi, and have little potential to cause disease. Biofilm formation is enhanced by many factors. Water stagnation occurs when the dental unit is not in use, which facilitates accumulation of bacteria. Even when the water in the tubing is flowing during use, it is not under high pressure, and the flow rate is very low near the tubing walls. The bacteria that enter the tubing are able to adhere to the lining of the tubing and then multiply.