Common causes of backflow include changes in water pressure within the plumbing system, such as during water main breaks, firefighting activities, or sudden demand surges. Backflow can also occur due to back siphonage, where negative pressure in the plumbing system draws water from a non-potable source, such as a garden hose left in a pool or a chemical tank.

Additionally, cross-connections between potable and non-potable water sources, such as irrigation systems or boilers, can lead to backflow if not properly protected. These factors can compromise the integrity of the clean water supply, highlighting the importance of backflow prevention measures.