What happens if the pressure in a potable water system falls below atmospheric pressure?

When the pressure in a potable water system falls below atmospheric pressure, it creates a condition that can lead to backflow. Backflow refers to the unwanted reverse flow of water, which can occur when the pressure in the supply line drops significantly, allowing water from the surrounding environment, including potentially contaminated water, to flow back into the potable water supply. This is particularly concerning in plumbing systems, as it poses a serious risk of contamination of the drinking water.

Maintaining proper pressure in the water system is essential for preventing backflow. When the pressure is compromised, devices such as backflow preventers are critical to protecting the system; however, if these preventative measures fail or are not in place, backflow can occur, leading to contamination of the water supply.

The other scenarios provided, such as fixture functionality or system clogging, do not directly result from a pressure drop below atmospheric levels in the same way as backflow does. Therefore, the primary concern with a drop in water pressure in a potable system is indeed the backflow of water.