What can cause backflow in a water system?

Backflow in a water system occurs when the normal flow of water is reversed, allowing contaminants to enter the potable water supply. This can happen through two primary mechanisms: back pressure and back siphonage.

Back pressure is created when the pressure in a downstream system exceeds the pressure in the supply line, often due to pumps or an external source of pressure. This can force contaminated water from a local system back into the main supply line.

Back siphonage occurs when there is a drop in pressure in the supply line, such as during a heavy demand period or a water main break. This negative pressure can create a vacuum effect, pulling water from the adjacent systems (that may be contaminated) into the clean water supply.

Therefore, the correct answer acknowledges that both back pressure and back siphonage can cause backflow. Addressing both phenomena is crucial in designing and implementing effective backflow prevention measures in any water system. Other options either consider only one mechanism or suggest a scenario that does not encompass the true risks associated with water supply systems.