Cross-connections should be eliminated where possible; if a cross-connection cannot be eliminated, it must be controlled by installing an appropriate back flow preventer. With these principles in mind, the authority having jurisdiction can make informed decisions related to cross-connection control and the protection of the drinking water system. A drinking water system is protected when the correct backflow preventer is selected by considering various risk factors including the degree of hazard, the probability of occurrence, hydraulic conditions, and the functional limitations for each type of backflow preventer.