Question 51

The Correct Answer is A. **Explanation of Option A (To stop insects from entering):** Screens (or wire mesh) on the vents of potable water storage tanks act as a physical barrier. Their primary purpose is to prevent contaminants, such as insects, rodents, birds, and windblown debris (e.g., leaves, dust), from entering the tank. Insects, in particular, can enter small openings, and if they die or deposit pathogens in the water, they compromise the water quality and public health. This barrier function is a mandatory requirement in almost all water industry standards and regulations (e.g., AWWA, state health departments). **Explanation of Incorrect Options:** * **B) To prevent explosions:** Vents are designed to allow air exchange during filling and withdrawal (preventing a vacuum or excess pressure), but screens do not prevent explosions. Explosions are prevented by ensuring tanks do not accumulate flammable gases, which is unrelated to the mesh screen itself. * **C) To filter the incoming air:** While the screen physically blocks large particulate matter, it is not considered an effective air filter for microscopic contaminants like dust, pollen, or pathogens. True air filtration requires a much finer filter media than a standard protective screen. The primary function remains pest and debris exclusion, not comprehensive air purification. * **D) To prevent backups:** The function of the vent is to allow air *into* and *out of* the tank to equalize pressure. Vents do not manage the flow of water (which prevents backups); gravity, pumps, and overflow systems handle that. Screens on the vent have no role in preventing water backups.