Water is a fundamental, but often neglected part of any building hygiene program. Water is used for cooking and washing, as well as in heating systems, air conditioning and cooling systems. It is not surprising to find, therefore, that water is one of the foremost methods of transmitting bacterial or viral infection. While great care and attention may, rightly, be paid to kitchen hygiene and physical cleanliness, often, very little care will be taken to maintain the integrity of hidden aspects of a water system. The costs associated with outbreaks of water borne infection, such as Legionnaires Disease, Norwalk Virus and Gastroenteritis are significant.