Why Backflow Is a Major Health Hazard
When backflow is not controlled properly in a building, the drinking water supply can be contaminated with hazardous substances and waste. This can affect not only occupants in the building, but also neighboring properties that use the same water service. In general, backflow will occur when there is a reverse pressure in the plumbing system, and no devices to prevent water movement. There are two ways this can happen - backsiphonage and backpressure.
Backsiphonage occurs when water pressure is lowered upstream, creating a pressure difference that pulls water towards the source. This is often caused by fractured or undersized pipes, especially when water consumption is high. Back siphonage can also occur when fire hydrants are opened, causing the water supply pressure to drop suddenly.
Backpressure occurs when water pressure is raised downstream. Just like back siphonage, this condition creates a pressure difference towards the water supply. Back pressure can be produced by gravity in high-rise buildings, and by pressurized installations such as automatic sprinkler systems.