A cross-connection is a pathway for backflow of non-drinking water into the drinking water system. Backflow can occur either because of reduced pressure in the drinking water system (called backsiphonage) or the presence of increased pressure from a non-drinking water source (called backpressure). Backsiphonage may be caused by a variety of circumstances, such as main breaks, flushing, pump failure, or emergency firefighting water drawdown. Backpressure may occur when the pressure in the external customer system exceeds the pressure in the drinking water system. Both conditions act to change the direction of water, which normally flows from the drinking water system to the customer, so that non-drinking water and potentially contaminated water from industrial, commercial, or residential sites flows back into the distribution system through a cross-connection.