Backflow is caused by cross-connections that have the potential of allowing contaminants into the drinking water system. Back siphonage can occur when the pressure in a tank or water trough is lower than the water system’s pressure. This could allow the influx, or pulling, of contaminated water into the system...

Another cause of backflow is back pressure. Back pressure occurs when there is higher water pressure in a fire protection system or in a multi-story building that contaminated water could be forced into the public water system.