August, 2006
Inspection News and Views from the American Society of Home Inspectors

More Straight Talk About Cross-Connections


In April of 2000, the ASHI Reporter published my first submitted article “Straight Talk about Cross-Connections.” Since that time, ASHI has been kind enough to print several of my articles, and, in some ways, help me get my work published in other trade journals and magazines.

Much has changed with the Reporter since the year 2000. A more professional look that now includes color photos has made it an award-winning publication. Many other things also have changed since 2000, including the urgency for better cross-connection control and cross-connection education. Today, it is not uncommon to see information on cross-connections included in reports on biological and chemical terrorism. Typically, it’s pointed out how cross-connections will compound such an event or even be used to facilitate it. The fact is, since 9/11, cross-connections have gone from being an issue dealt with by the local purveyors of drinking water to a national and even international concern.

I recently reviewed my first cross-connection article and thought how the information is still relevant, even timely, and would be well worth repeating. With the addition of color to the ASHI Reporter, I felt some photos could make the information more understandable, and make cross-connections and the various protection devices employed to combat it more recognizable. The Reporter staff agrees and has allowed me to rework and update my first article.

Cross-connections and backflow
Watts® Water Technologies, a manufacturer of numerous plumbing, safety and backflow devices, defines a cross-connection as “a direct piping arrangement of a piping line that allows the potable water to become connected to a line that contains a contaminant.”

The major plumbing codes prohibit cross-connections to the potable plumbing system except when an approved protective device is installed.

There are many documented cases where cross-connections are said to have caused people serious illness and injury. The cross-connection itself is not the cause of the illness or injury, but is the conduit or the pathway by which water contamination takes place during an event known as backflow.

There are two types of backflow. Back-siphonage backflow begins when normal flow is reversed due to a vacuum or partial vacuum. Drinking through a straw and siphoning gasoline from a car are good examples of back-siphonage.

On the other hand, back-pressure backflow is created when the pressure downstream becomes greater than and overwhelms the supply pressure. Boilers are prone to this condition. I’ll get more specific later.

Putting backflow into motion can begin in many ways. For buildings on a public water system, a water main break or a fire truck pulling on a fire hydrant can start a backflow event. A malfunctioning water pump that supplies water to a building on a private water source can cause a backflow as well.

Because backflow events can be unpredictable, it’s important to try to eliminate all cross-connections from our potable water systems. However, this can sometimes be impossible or impractical. Therefore, when a cross-connection or potential cross-connection is placed in the system, protective devices, called backflow preventers, should be installed to help prevent cross-connection contamination from occurring.

The degree of hazard
The substance drawn into the potable water system can be toxic or non-toxic. With residential properties, this could be anything from a little rusty water or antifreeze found in a boiler to raw sewage from a drain. Pesticides and fertilizers are big offenders as well. When determining the level of the protection device, the toxicity level of the potential contaminant is a major concern. All devices or protection methods are rated. Some are rated for “low hazard level only.” Some are rated for “high or low hazard protection.”

Plumbing codes or municipalities usually determine the device or method used to provide protection against a cross-connection. Some municipalities require regular inspections of installed devices, testing and even certification of the individuals performing the tests. In Virginia, my home state, certified backflow device testers are usually plumbers, mechanical contractors, irrigation and fire suppression workers and they carry the certification in addition to their trade licenses.

Protection methods and devices
The methods or devices, sometimes referred to as the products of cross-connection protection, are defined by Watts® as follows:
  1. Air Gap
  2. Atmospheric Vacuum Breakers- which include hose connection vacuum breakers
  3. Pressure Vacuum Breakers-which include backflow preventers with intermediate atmospheric vents for 1/2" and 3/4" lines
  4. Double-Check Valve Assembly
  5. Reduced Pressure Zone Backflow Preventers
Since my first article was published in 2000, I have learned of another method of protection called a barometric loop. The barometric loop incorporates the use of an inverted U-tube. On one end, the water supply enters a plumbing line and rises to a height of 35 feet. The line flattens out on top and then drops downward. An opened receptacle located at the bottom of the plumbing line is filled by the water line pressure. However, if the pressure is interrupted and a siphoning action develops, the receptacle cannot be siphoned as the water is incapable of rising to that height while at sea level.

I can think of no practical use for this method of backflow protection on residential properties, but it might find some use for some commercial applications or on a ranch or farm.

Inspecting for cross-connections during a home inspection
Probably the most obvious cross-connection observed by home inspectors, especially those who work older properties, is that of the tub spout located below the rim of the tub. On some older tubs, not only is the spout located below the tub rim, but the entire faucet might be found there as well.

Bath1.gifWith below-the-rim spouts, back-siphonage backflow is the concern. During a backflow event, suction on a submerged spout can pull in dirty bath water, allowing it to mix with the freshwater system. Your first thought here might be, “that’s disgusting, but not necessarily deadly,” and this is true. But now fill the tub with sewage from a blocked sewer main and the situation becomes very serious.

With some new specialty tubs, below-the-rim spouts are being installed again. However, before noting this as a defect on your inspection report, be sure to check around the tub or check the faucet closely for a backflow preventer, such as a vacuum breaker, that might be connected to the spout. Writing this up as a defect, only to have a plumber point out the location of a backflow preventer, can be embarrassing. However, if you’re concerned a cross-connection exists, note your concerns in the inspection report.

As for the older tubs, if you determine that the setup is indeed a cross-connection, relocation of the spout is not always the only remedy. With the availability of different backflow devices, there are methods of making this arrangement backflow-safe while maintaining the antique look of the fixture. To do this work, your client might have to find a more experienced or creative plumber.

Bathtub and shower attachments
The spout located below the rim of the tub is not always your only concern for a cross-connection between the drain water and potable water at bathtubs. There are a number of hand sprayers and shower massage units that could also be a concern. If the hand sprayer’s hose reaches a level that puts the hand piece below the tub rim, you should examine the sprayer assembly closely for a vacuum breaker.

Vacuum breakers that are an integral part of the sprayer are located above the tub, generally near the plumbing connection at the wall. When the sprayer is in use, the vacuum breaker allows water to flow through the hose with little notice. If the water is interrupted, it prevents siphoning from a hand piece left in the tub. In many cases as the water is turned off the sprayer, you will hear the device sucking air and sometimes it drips. If the vacuum breaker is installed in a fashion that allows it to be submerged in the tub, it is likely to be ineffective, as it needs air to function.

When no device can be found, write it up as a potential cross-connection. It has been my experience as a plumber and former Realtor® that it is unlikely the client will replace it right away, if at all, but as a home inspector, I still recommend noting the concern and cautioning the client to always keep the sprayer secured and out of the tub when it is not in use.

When an anti-siphon or code-approved ballcock or fill valve is not used, a toilet can become a cross-connection concern. Today, toilets are sold with “code-approved” parts, but repairs with unsafe parts are made daily.

Home inspectors who inspect tank parts should pay close attention to the cutoff point of the ballcock when inspecting the tank works. In most cases, the cutoff will be above the water level and is likely to be an approved valve. Ballcocks with the cutoff below the water, such as the old Fluidmaster model 200 ballcock (bottom left), are likely offenders for sending tank water into the potable water during a backflow event.

This particular ballcock was an extremely popular device sold for many years. It was inexpensive, easy to install, and, because repair parts can still be purchased to repair one that develops a leak, you can still find them installed in older toilets today. The manufacturer claims it no longer sells the 200 and it can be easily replaced. The model 400A is also inexpensive and easy to install, but with this ballcock(bottom right), the cutoff is located above the tank’s water level.

Since plumbers occasionally get calls from customers complaining of drawing blue water from a lavatory faucet, it is likely that the consumption of tank water occurs more often than we realize. For every tank containing blue sanitizers, certainly there are many more than do not. Compared to other potential contaminants, this water is relatively clean, but there are better places to get a refreshing drink. Check the ballcock closely.

Photo: Ballcocks with the cutoff below the water, such as the old Fluidmaster model 200 ballcock, are likely offenders for sending tank water into the potable water during a backflow event.

Photo: The Fluidmaster model 400A is also inexpensive and easy to install, but with this ballcock, the cutoff is located above the tank’s water level.


Generally found in more upscale homes, a bidet is a plumbing Bidet-Kohler.giffixture that is susceptible to back-siphonage backflow. Because it’s mounted to the floor and sat on when in use, this plumbing fixture is often thought of as a toilet. But, in fact, a bidet is a
specialized use sink. It is supplied with hot and cold water, has an external trap and sometimes a pop-up waste.

Cross-connection becomes a concern depending on how the bowl is filled. A deck-mounted faucet with an over-the-rim spout or nozzle is considered backflow safe. However, if the bowl is filled from below the rim with a douche sprayer or jet, a backflow device should be installed.

The backflow device for this fixture will likely be an atmospheric vacuum breaker. Look for a device to be mounted at the faucet end of the fixture above the overflow rim of the bowl. The
vacuum breaker will be plumbed in the plumbing line that carries the mixed water to the below-the-rim filler, douche nozzle or sprayer. Sometimes, the vacuum breaker will be attached to the faucet or mounted on the wall nearby.


Photo: Kohler® deck mounted bidet faucet


Photo: Kohler® bidet faucet with vacuum breaker

Vacuum breakers leak, so be careful when filling the bowl for inspection. Dripping water from a vacuum breaker can cause damage to the structure, as well as be an indicator of an ineffective or malfunctioning device.

Laundry tubs or mud sinks
Before washing machine service boxes, laundry tubs actually provided a means of supplying water and drain facilities to washers. Hose bib connections, sometimes located below the rim of the tub, provided hot and cold water to the machine. The drain hose hung over the side of the tub and discharged into the sink.

In later years, when washing machine hoses were removed and attached to more modern service boxes located behind the machines, the sinks provided a convenient place to soak soiled laundry, clean paint brushes or wash up after a hard day at work. But these sinks with their below-the-rim valves or hose-threaded spouts also are potential cross-connections.

Trash.gifBecause they are often installed in basements, putting them below much of the DWV system, they can become awash with sewage and other waste products during a system backup. Because they are sometimes forgotten, the sinks can become a collection point for trash and even chemical waste. But as long as they are still connected to the plumbing system, they are capable of contaminating the potable water system in a serious way.

Though not all abandoned fixtures are potential cross-connections, other health risks could be present. Dangerous and unpleasant odors are likely to enter through unsealed traps. Insects and other vermin are often found around these fixtures as well. When a plumbing fixture is no longer in use, it should be professionally capped off from the system.

Today, architects and builders have renamed these service sinks “mud sinks,” and it’s unlikely you’ll find any part of the faucet located below the rim. However, some new faucets often incorporate the use of a hose-threaded spout. Unless a vacuum breaker is an integral part of the spout, a hose bib vacuum breaker should be added to make it cross-connection safe. Sometimes, the spouts can be replaced with one that has an aerator or screen instead of a hose connection. Hose threads can also be cut off to prevent the easy installation of a hose.

Hose bibs and sillcocks
One of the most potentially hazardous plumbing devices found at a residential property is an unprotected sillcock or hose bib. Because of its versatility, the sillcock can be connected to anything from a fertilizer sprayer to a container of weed killer. Left unprotected, chemicals can be drawn through the valve and into the freshwater system.


Photo: Unprotected sillcock. Photo courtesy of Watts®

In my first article, I spoke of a mishap between an exterminator, a chemical tank and a city water main repair. Since then, I have learned several more things about the incident, and I would like to make a few corrections.

According to documents written by Lou Allyn Byus of the Illinois Environmental Protection Agency, it appears the incident took place in my state, Virginia, in October of 1979, not 1981 as I previously noted. Several accounts confirm that an exterminator’s hose attached to an unprotected sillcock and submerged in a tank of chlordane did provide the conduit for a serious backflow event. The chemical reportedly moved through the hose, the house supply line, and eventually was discovered dripping at an opened water main under repair in the city street.

I noted in my earlier article that, because of the contamination, some residents went without water for more than a month; however, some Internet accounts say the actual time was closer to two months. As for damages, it appears I might have come up a little short on the damages. By one account, the city involved in the incident paid $250,000 for replacement and repair costs. The exterminator paid the city $70,000. As much as $160,000 in additional lawsuits was paid out by the exterminator and the employees. Out-of-court settlements were reached by some residents for even more money, and a $20,000,000 class action settlement also resulted from the incident.

Photo: A Watts® hose bib vacuum breaker.

The bottom line here is simple. The next time you’re asked during a home inspection if a missing hose bib vacuum breaker is a big deal, tell your client about this case. Then, remind the client that an inexpensive hose bib vacuum breaker likely could have prevented this disaster.

By far, the condition that causes most backflow in the average home is back-siphonage. However, when the equipment used to heat or cool the home is connected to the potable water service, it could also be susceptible to backpressure backflow. Though other equipment exists, the best-known heating equipment connected in this manner is a boiler.

The average hot water boiler operates at between 15 to 20 psi of pressure. The water pressure is controlled or regulated by a pressure-reducing valve connected between the boiler and a cold water distribution line. Since the average home’s domestic water pressure is two or three times the boiler pressure, under normal conditions there is little chance of the boiler water mixing with the house water. But if the house pressure is drastically reduced or interrupted, the boiler pressure could exceed the house pressure, and it’s possible the boiler’s water, along with any contaminants, could move to the house side of the system.

Though a quality pressure-reducing valve has a built-in check valve device, it typically does not qualify as a backflow preventer. A dual unit combines a
pressure-reducing valve and a relief valve to make a convenient package for installers. It provides pressure reduction for boiler operation and pressure relief for safety, but, again, does not provide true backflow protection. It has been my experience that the relief valve is sometimes mistaken for a backflow preventer with this combination control.

Photo: A dual unit combines a pressure-reducing valve and a relief valve to make a convenient package for installers.

There are several devices that can be used here to protect against cross-connection contamination, but one device was specifically designed for the job, and it gets high praise from mechanical contractors. A Backflow Preventer with Intermediate Atmospheric Vent provides a combination of check valve and vacuum breaker-type protection, and it does so at a competitive price. The Watts 9D is a popular Backflow Preventer with Intermediate Atmospheric Vent product.

Photo: The Watts® 9D is a popular Backflow Preventer with Intermediate Atmospheric Vent product.

When inspecting a hot water boiler system, always look for backflow protection. The device should be located somewhere between the pressure-reducing valve and the water service connection. When installing a Backflow Preventer with Intermediate Atmospheric Vent, a common mistake is to locate it on the low pressure side of the system. When installed on the low side, the device will typically drip water from the vent as it needs about 25 pounds of pressure to function properly. Because of the drip, the vent gets plugged. Installing the device on the low side of the system and/or plugging the vent can keep the backflow preventer from working properly. Be sure to recommend further evaluation by a qualified professional if you discover an improperly installed, plugged, dripping or missing backflow preventer on a hot water boiler system.

Lawn irrigation systems
Although many home inspectors stay away from evaluating lawn irrigation systems, those who do check them should be familiar with specific cross-connection concerns and protection devices. As with everything else discussed in this report, the localities generally regulate in some way the installation of lawn sprinkler systems. This is especially true if the system uses water supplied by the municipality. However, because many of these systems are often bootlegged in place, I find that a proper inspection by a code official is pretty rare and cross-connections are quite common with irrigation systems.

When an irrigation system is independent of the potable water supply, or, in other words, on its own well, the impact of a contamination is generally not as severe as one that is tied to the potable source. If the house pressure is interrupted on a city connected system, there is the potential for contaminated water to be sucked from lawn puddles through opened sprinkler heads and deposited into not only the house supply, but into the city lines themselves. Fertilizers, animal wastes and mites are just a few of the contaminants that can be drawn into the system.

With improvised work, it is not uncommon to find an irrigation system connected to both the city supply and a well source separated by a hand valve. Here you risk not only contamination from back-siphonage, but from backpressure backflow as well. Should the hand valve be left opened, slightly opened, or if it leaks between the two systems, they can mix. If the well system’s pressure exceeds the city pressure, any contaminant on the well side can not only move into the city side, it also could be forced into and down the city main. In this case, contaminated water could be consumed by others on the system.

Some localities do install dual-check valves at the meter to prevent this from occurring, but many do not. Also,
because dual-check valves are not testable, you can never be certain they are working properly.


Photo: A Watts® dual-check valve

A properly protected cross-connected residential irrigation system will likely use one of two devices—an atmospheric-vacuum breaker or a pressure-vacuum breaker. Localities, codes and the location of the zone control valves generally determine the device used.
An atmospheric-vacuum breaker is often used on systems when shutoff valves or zone controls are not found downstream. This way, it is not under pressure when the system is not operating. With this product, a separate vacuum breaker might be used on each zone instead of an entire system.


Photo: A Watts® atmospheric-vacuum breaker

A pressure-vacuum breaker is often used when control valves are installed downstream and when one control is wanted for the entire system. Both units must be mounted above the sprinkler heads, and a pressure-vacuum breaker should be periodically tested. Ports are provided so test gauges can be attached by the tester.


Photo: A Watts® pressure-vacuum breaker

Even if you don’t inspect irrigation systems, consider checking the supply piping to see if the lawn irrigation system is physically separated from the potable system. A shutoff valve between the two systems does not qualify as physically separated.

When the systems are connected, check to see if there is a backflow device in place between the two sides. If a backflow device is present, note if the device is readily accessible. If it is leaking, consider it defective. If the device appears to be testable, recommend periodic testing by a qualified tester and explain to your client that without testing, it is impossible to tell if the device is functioning properly. In my area, not only is annual testing required, but the city will alert the owner when test results are due and will discontinue water service if it is not done in a timely manner.

ASHI Standards of Practice and cross-connections
The current Standards do not specifically mention cross-connections as a defect to be observed and reported to the client. The inspector is expected to inspect all aspects of the plumbing system and to report the findings. Just as reporting leaks and poor functional flow are a part of a complete plumbing inspection, cross-connection identification is a major part of the home inspector’s job.

Unlike leaks and poor functional flow, recognizing cross-connections requires more thought. I encourage you to read more about cross-connections and backflow. Information is readily available in print and on the internet, and, as always, I am happy to answer your e-mails if you have questions on the subject.

As with the first article, I would like to thank Watts® Water Technologies for their contribution of information and many of the photos used in this article.


Commonly Used Backflow Methods and Devices

Air Gap

The distance between the spout outlet and the overflow rim of a sink or other plumbing receptacle is known as an “Air Gap.” It is the most widely used and effective method of cross-connection protection since contaminated drain water cannot reach the spout without running over the top of the receptacle being filled.

Atmospheric-Vacuum Breakers

For residential use, atmospheric-vacuum breakers are
commonly found on certain irrigation systems, bidets, hose-threaded faucet spouts and sill cocks. 




Pressure-Vacuum Breakers

Pressure-vacuum breakers are commonly found on irrigation systems. The category also includes backflow preventers with intermediate atmospheric vents manufactured for use on boilers. The pressure-vacuum breaker at the lower left has a port so gauges can be attached for periodic testing. Testing is required by some municipalities to ensure proper operation. The backflow preventer with intermediate atmospheric vent, which is primarily used on boilers (bottom photo), is not testable.



Double-Check Valve Assemblies

There are many variations of the double-check valve assembly. It is commonly used in commercial applications for building containment, irrigation systems and fire suppression systems. The device is testable.


Reduced Pressure Zone Backflow Preventers

There are many variations of the reduced pressure zone backflow preventer. Used in many commercial and some residential applications, RPZ devices can be used for building containment, boiler and other equipment protection and is testable. It is a very popular backflow preventer. It appears similar to the double-check valve assembly, but has a relieve opening at the bottom of the device.

The Barometric Loop

In physics, we learned that at sea level pressure, a
column of water opened at the bottom will not rise above 33.9 feet. The barometric loop will protect against back-siphonage only and has no practical use for residential properties.


Author’s note: I have never seen this method used for backflow protection. However, I was informed
that it’s sometimes used to protect potable water from livestock drinking troughs on ranches and farms.