Vents are installed in aboveground, covered water reservoirs and in underground reservoirs to allow ventilation of the stored water. Specifically, vents permit the passage of air that is being displaced from, or drawn into, the reservoir as the water level in the reservoir rises and falls due to system demands. Small reservoirs may require only one vent, whereas larger reservoirs may have multiple vents throughout the system.

While the specific vent design for any given application will vary depending on the design of the reservoir, every vent consists of an open air connection between the reservoir and the outside environment. Although these air exchange vents are an integral part of covered or underground reservoirs, they also represent a potential security threat. Improving vent security by making the vents tamper-resistant or by adding other security features, such as security screens or security covers, can enhance the security of the entire water system.


Many municipalities already have specifications for vent security at their water assets. These specifications typically include the following requirements:

Some states have adopted more specific requirements for added vent security at their water utility assets. For example, the State of Utah?s Department of Environmental Quality, Division of Drinking Water, Division of Administrative Rules (DAR), provides specific requirements for public drinking water storage tanks. The rules for drinking water storage tanks as they apply to venting are set forth in R309-545-15: "Venting," and include the following requirements:

In a second example, Washington State's "Drinking Water Tech Tips: Sanitary Protection of Reservoirs" document states that vents must be protected to prevent the water supply from being contaminated. The document indicates that non-corrodible No. 4 mesh may be used to screen vents on elevated tanks. The document continues to state that the vent opening for storage facilities located underground or at ground level should be 24 to 36 inches above the roof or ground and that it must be protected with a No. 24 inch mesh non-corrodible screen. New Mexico's Administrative Code also specifies that vents must be covered with No. 24 mesh (NMAC Title 20, Chapter 7, Subpart I, 208.E).

As described above, both Washington and New Mexico, as well as many other municipalities, require vents to be screened using a non-corrodible mesh to minimize the entry of insects, other animals, and rain-borne contamination into the vents. When selecting the appropriate mesh size, it is important to identify the smallest mesh size that meets both the strength and durability requirements for that application. (Note: mesh screens are measured based on the number of openings per linear inch of screen. The higher the mesh number, the smaller the openings, and therefore the better the protection against possible intrusion of dust, dirt, animals, insects, etc.).

Several additional features and attributes that can enhance vent security are discussed below.

Vents must be designed to withstand physical attacks and to defend against contamination of the reservoir. The discussions below summarize the features and attributes that manufacturers have designed into vent systems to mitigate these various types of threats.

Manufacturers have been designing new vents from strong materials, such as stainless steel. Constructing the vent from these types of materials increases the vent's resistance to physical tampering. For example, the ARC3 Corporation's security vent is typically constructed from heavy-gauge carbon or stainless steel; however, other materials (i.e., plastic, fiberglass, Kevlar, etc.) may be used to construct the vent as long as they are compatible with the vent?s application.

Recent innovative vent designs restrict the entry of solid or liquid contaminants into the vent while allowing the movement of air into and out of the reservoirs. For example, one vendor has designed a cover for cylindrically-shaped vents that incorporates a series of cylindrical barriers anchored to the cover. The configuration of this security air vent creates a convoluted path between the interior of the reservoir and the exterior atmosphere. The barriers are arranged concentrically, and consist of an outer baffle (first barrier), an inner baffle (second barrier), a base plate (third barrier), and a top plate. Any substance entering the vent is forced to flow between the barriers in series. Specifically, as the substance flows into the vent, it hits the outer baffle, which forces it up towards the top plate. As it hits the top plate, it is directed downward by the inner baffle, where it hits the base plate and is again directed upward and into an open connection with the reservoir. When pressure inside the tank is greater than pressure outside the tank, the flow is in the opposite direction.

Another security air vent designed for use on louvre-type vents utilizes an arrangement of S-shaped structural members, which allow the movement of air but restrict the passage of liquids or solids, even if the liquids or solids are applied under force or pressure. Each of these structural members helps to dissipate the energy of the contaminant flow, and as the forward momentum energy weakens, gravity causes the contaminant to drop out and drain to the exterior.

Both of the designs described above are patent-protected with the U.S. Patent Office and are commercially available.

There are several other basic measures that can enhance vent security, such as anchoring the vents with corrosion-resistant stainless steel connectors and bolts, covering vent openings with non-corrodible mesh screens, ensuring that the vents are inverted or shielded from surface or rainwater, and ensuring that the vents are not located in an area that will be susceptible to blockage. Implementing these measures may aid in mitigating both accidental and intentional contamination of a water asset through the vent.

Municipalities looking to enhance the security of their reservoir vents may also wish to monitor security enhancements developed for underground storage tank vents, because these security enhancements may be able to be implemented on reservoir vents.

Vents can also be equipped with an optional intrusion alarm system to notify appropriate personnel when the vent is disturbed. For more information on intrusion alarms, please refer to the Alarms Product Guide.

It should be noted that vents with upgraded security features can be installed new or retrofitted over existing vent pipe structures. Manufacturers have created variously-sized retrofit security vent designs that can be fit over existing vent pipes. For instance, one vendor manufactures vents in four sizes that will fit existing vent pipe diameters of 6 to 8, 10 to 16, 18 to 24, and 30 to 36 inches, respectively.

The primary factors affecting cost of security vents are the vent size (the larger the vent, the higher the cost) and the type of material from which the vent is constructed (i.e., vents constructed from carbon steel will be less expensive than vents constructed from stainless steel). For example, one vendor sells a security cover for a 10- to 16-inch diameter vent for approximately $3,730, while a cover for an 18- to 24-inch diameter vent would cost approximately $5,350. At present, security air vent for louvre-type vents are only manufactured for custom-fits into existing reservoir structures. Costs for these vent covers are dependent on the type of structural material required and the size of the existing vent openings.