Val-Matic’s white paper Protecting Drinking Water Pipelines with Inflow Prevention explains this in more detail. With the heightened demand for security and safe drinking water, inflow prevention is important because air valves and reservoir vents are vulnerable to flood contamination as well as malicious tampering.
The use of vent pipes can worsen the problem by allowing cold air to enter the valve and potentially make it inoperable due to freezing and directly exposing the pipeline to the outside and malicious tampering. AWWA C514 Inflow preventers can be applied to new or existing air valves and reservoir vents to substantially mitigate these threats.