Informed design professionals who understand the basics of backflow prevention are able to successfully manage regulations and safely deliver fresh drinking water in their projects. The common response from several architects when asked about the importance of backflow protection was that they “left that up to the mechanical engineer.” These professionals were experts in green design and knowledgeable about the basics of best practices for water conservation. Among them, only a few mentioned their concern for the placement of plumbing controls, maintenance schedules, the locations of access panels, fire safety systems, and cross-connection controls. Reviewing the basics of cross-connection and backflow controls will allow them to partner with their mechanical and plumbing engineers and create strong design teams that will protect drinking water.

All images courtesy of WATTS Water Technologies, Inc.

Cross-connection controls are critical to the protection and conservation of drinking water. The health, safety, and welfare of the public depend on the appropriate design and planning of cross-connection controls in buildings and landscape projects.

The resiliency and safety of a drinking water system may be assured through a basic understanding of the cross-connection controls. These mechanical controls provide the barrier between pollutants and the public supply of fresh drinking water. This course will review the basics of these important mechanical devices, from simple vacuum breakers to detector assemblies for fire sprinkler systems. These devices are usually specified by engineers and added to a project manual with little understanding as to how a lack of knowledge can lead to an overly complicated project delivery.

The early analysis of cross-connection controls includes many advantages to the design professional. These include improved designs for mechanical rooms, better project scheduling, safer site infrastructure, easier permitting, and proper equipment maintenance. An architect who assembles complete project delivery teams will include civil (site infrastructure), mechanical, and plumbing engineers. These professionals should be involved in project planning from initial programming through construction documentation and commissioning.

Protecting Drinking Water from Contaminants

The public water supply is distributed by a series of pipes, storage facilities, and conveyance components. Since the 20th century, these distribution systems are designed and regulated to provide an uninterrupted supply of pressurized safe water to consumers. According to the U.S. Environmental Protection Agency (EPA), public distribution systems span almost 1 million miles in the United States, representing the clear majority of physical infrastructure for water supplies. In addition, public water systems meet fire protection needs for cities, homes, schools, hospitals, businesses, and industry.

Shown are typical locations of check valves and appropriate backflow prevention systems in a commercial building.

Cross-Connection

A cross-connection, as defined by the EPA, is “any actual or potential connection between the public water supply and a source of contamination or pollution.” Such cross-connections constitute a hazard to the building occupants and can jeopardize the cleanliness and potability of the public water system in the event of a backflow or backsiphonage event. An actual connection is a direct connection to a source of contamination, such as an unprotected boiler connection. An example of a potential connection could be as simple as a hose bib, which could potentially be connected to a pesticide sprayer.

Backflow

Backflow is the unwanted and potentially dangerous reverse flow of liquid, gas, or another substance into a potable water distribution system. According to the EPA, “most backflow incidents are generally detected and reported to the local authority only if customers detect an irregularity in their water supply...but not all contamination that produces illness and disease can be detected by taste, color, or odor.” Each plumbing system is unique, and often contamination is not identified until serious symptoms occur. Backflow can occur outside from hoses, pools, and other exterior equipment, as well as from equipment inside buildings.

Backsiphonage

Backsiphonage is a condition that occurs whenever there is a negative or subatmospheric pressure in the potable supply piping. These conditions typically occur during periods of very high demand in the public water main, which lowers the supply pressure. In some cases, demands imposed by firefighting operations (or in the event of a water main break) will suddenly and significantly lower a city’s water pressure below atmospheric pressure. This pressure change results in a partial vacuum being drawn on the non-potable system. This vacuum will siphon the pollutants or contaminants into the potable water system through an unprotected cross-connection, such as a hose bib or hydronic system make-up connection.

Backpressure

Backpressure is a push from the demand side. This occurs when pressure in a non-potable system is elevated above that of the potable supply, resulting in reverse flow. The installation of pumps, boilers, or other water heating equipment that may cause thermal expansion can results in reverse flow.

Cross-connection controls are critical to the protection and conservation of drinking water. The health, safety, and welfare of the public depend on the appropriate design and planning of cross-connection controls in buildings and landscape projects. This primer will provide an overview of the equipment, testing and permitting processes for cross-connection protection to ensure that public water systems will stay safe.

Degrees of Hazard

Backflow into the public water distribution system can be prevented by eliminating cross-connections or adding backflow preventers. According to the EPA, backflow is not only a threat to the health of our community, but it can also cause damage to our environment. The EPA recognizes that backflow incidents can cause issues such as corrosion of equipment, harmful microbial growth in our distribution systems, and changes in taste, odor, and color of the water supply. Chapter 3 of the EPA’s Water Quality Standards Handbook provides definitions and guidelines for water quality criteria.¹ Backflow risks are described as one of two types of hazards. A “pollutant” is any substance that may affect the color, taste, or odor of the potable water but does not pose a direct threat to human health through exposure or consumption of the water. Pollutants may impose an objectionable odor or appearance to the water, but they do not in and of themselves pose a health threat and therefore are considered to be a low hazard, or non-hazard, when compared to contaminants.

A “contaminant” is any substance that, when introduced into the potable water system, constitutes a direct threat to life or health of a human. This can occur through consumption or if the substance is in contact with the skin. A contaminant can be a caustic chemical, a fluid containing bacteria or disease, or any other substance that could threaten human health. Contaminants compose the highest degree of hazard to the potable water system.

The initial stage of an architect’s project is programming. During programming, design professionals analyze the proposed or future uses of a facility and possible connections to water supplies. This is particularly important when reviewing the cross-connections to public water supplies. The selection of backflow prevention system depends on whether the programmed use within a project is considered a low hazard, a non-hazard, or a hazard.

Preventable Backflow Failures

Public health officials have documented numerous incidents of unprotected cross-connections resulting in backflow. Plumbing equipment malfunctions, poor maintenance, and human error provide a litany of frequent opportunities for serious contamination of public drinking water. Many of these incidents are documented in the Cross-Connection Control Manual published by the EPA.² Some examples include the introduction of such contaminants as gas, blood, sodium hydroxide, heptachlor, pesticides, hexavalent chromium, and antifreeze in incidents that include the poisoning of the potable water in schools, hospitals, and large residential areas. The culprits include improper industrial tank pumping, broken water mains, community water main pressure reduction, frozen backflow preventers, hoses left in swimming pools, and improper gate valve installation. Contamination can occur at any point of connection between a potable water pipe and a source of non-potable water. Legionnaires disease can be caused by contamination from pathogens and bacteria introduced from cooling towers that have been installed or maintained improperly. The case study on the following page is an example of one incident of a preventable backflow failure.

The lack of hydraulic containment in hazardous areas led to serious illnesses and deaths in a health-care facility.