Backflow Prevention Practice Exam

A water closet ball cock must be installed above the opening of the overflow pipe by at least _____?

1. 1.0 in. (2.5 cm)

2. 2.0 in. (5.1 cm)

3. 2.5 in. (6.4 cm)

4. 3.0 in. (7.6 cm)

The correct answer is: 1.0 in. (2.5 cm)

The correct answer is that a water closet ball cock must be installed above the opening of the overflow pipe by at least 1.0 inch (2.5 cm). This requirement is established to ensure proper backflow prevention, which is critical for maintaining the safety and quality of drinking water. By installing the ball cock above the overflow, you create a physical barrier that helps to prevent any possible backflow of contaminated water from the toilet tank into the potable water supply. When the ball cock is positioned above the overflow pipe, it minimizes the risk of siphoning potentially contaminated water back into the clean water system, which could happen if the water level rises due to a malfunction. Ensuring that there is adequate separation between these components is a fundamental practice in plumbing standards aimed at safeguarding public health. Other choices reflect greater distances, but 1.0 inch is specified as the minimum required height, making it sufficient to achieve the necessary degree of protection against backflow in a typical installation scenario. Each additional inch offered in the other options does not change the minimum requirement for effective backflow prevention but could provide an additional margin of safety under specific conditions.