The question of dental unit waterline contamination now concerns the dental profession on a number of levels and has become part of the landscape in dentistry. Researchers have identified the problem, studied it, and published their results. Official organizations have reacted to the problem by issuing press releases and recommendations. In the mean time, dental companies have jumped into the fray, ensuring a proliferation of products designed to mitigate a problem that certain people feel is imaginary are artificially inflated. Despite the number of publications describing waterline contamination, we still face the challenge of determining whether are picture of the problem is truly accurate. For example, it has become almost customary to use the term contamination when talking about waterlines, even though it is inadequate. In addition, we are moving ahead with water quality standards for dental units at a time when certain fundamental questions remain unanswered. What should we be measuring and what methods should we be using? Do certain disinfection procedures have an opposite effect to the one desired? Finally, the question of health risks linked to the colonization of waterlines has not been adequately addressed by researchers.