Backflow can also occur in the absence of a water main pressure drop. For example, some customers have backup water systems connected to their homes’ plumbing. If these systems, supplied by private wells or springs, experience a pressure increase greater than that in the public water supply system, backflow will occur. Because these private supplies are not tested and regulated by governmental agencies, they may pose a hazard to the potable water system and must be equipped with proper backflow prevention devices.
