Backpressure backflow is a form of backflow due to pressure created by mechanical means or other means which causes water or other liquids or substances to flow or move in a direction opposite to that which is intended. Backpressure backflow is caused by a downstream pressure that is greater than the upstream or supply pressure in a public water system. Backpressure can result from an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both.
Causes of increases in downstream pressure: Pumps (such as wells and booster pumps), elevated tanks, temperature increases in boilers, etc.
Causes of decreases in downstream pressure: Water line flushing, fire fighting, or breaks in water mains.