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Overview Statement:  

This page includes detailed, need-to-know, information for residential water customers.

  • Is your water system at risk because of you?
  • Are you doing your part?
  • What’s the big deal?

What is a Cross Connection and what is Backflow?

Cross-Connection – is the physical connection between the potable (drinking) water system and an “end-use” (water utilizing fixture, equipment, or process) where a potential water contaminating hazard exists.

Backflow – is the undesired reverse flow of contaminants into the potable water from an “end-use” hazard and is typically driven by common, but unfavorable, hydraulic events in either the public or a private water distribution system.

Certified Cross Connection Tech List

Various Residential Water “End Uses” (How do customers use their water?):

Residential Plumbing Fixtures and Plumbing Appliances

Built-in Protection

Modern plumbing fixtures generally have built-in backflow protection. For instance, a faucet spout terminates above the flood rim level of the sink or tub. So if the sink or tub is full of dirty water or worse, backed-up sewage, there is no possible way for a backflow because of the air gap created by the elevated spout. Toilet fill valves, clothes washers, dishwashers, and refrigerator/ice makers also employ some type of built-in air gap as their method of protection.

Hand Held Sink or Shower Spray Heads

Hand held shower heads are required to be protected against backflow in one of two ways:

  1. When connected to a standard shower head gooseneck, and where the outlet (spray head with long hose) can be submerged, a vacuum breaker meeting product standard/listing ASSE 1001 shall be installed. 
  2. When the connection is below the flood rim level, as typically done with a deck mounted tub/shower combination valve, a dual check valve shall be installed on the delivery side of the main tub control valve or two dual check valves shall be installed in the hot and cold supply lines ahead of the main tub control valve. The Dual Check Valve(s) shall meet the product standard/listing ASSE 1024.

Vacuum Breakers and Dual Check Valves are considered “non-testable” and may be installed or replaced by a homeowner.

Kitchen and lavatory faucets, constructed within the US, with integral or auxiliary spray heads, generally do not need additional backflow prevention devices.

Hose Bibb and Garden Hose Usage

Because of their portability and universal ease of connection, general purpose/garden hoses pose one of the greatest risks for backflow occurrences. In addition, there is a general complacency (underestimation of hazard level), with what hoses are connected to or with what they are left submerged in.

In residential applications, the normal way to protect the drinking water system from the hose, and its uses, is to outfit the hose bibb (spigot/valve) with a vacuum breaker. Hose bibbs are available with integral vacuum breakers or vacuum breakers can be purchased separately and screwed directly onto the outlet threads of the bibb. In this case, the vacuum breaker, in turn, has hose threads to connect the hose to. Vacuum breakers are very inexpensive but provide a very good level of protection against backflow.

Every hose bibb, regardless of age or usage, must be outfitted with a vacuum breaker meeting the product standard/listing ASSE 1011 or ASSE 1019.

Vacuum Breakers are considered non-testable and may be installed or replaced by a homeowner.

In-ground Irrigation and Lawn Sprinkler Systems

Automatic irrigation systems pose a significant threat to the drinking water system. By their nature, sprinkler heads may reside in a pool of yard/animal waste, pesticides and/or fertilizers. And because the supply lines are under constant pressure and flow, and controlled by underground control valves, a typical vacuum breaker is not an appropriate form of protection against backflow. There are two types of backflow prevention assemblies allowed:

  1. Pressure Vacuum Breaker (PVB) – ASSE 1020; this assembly must be able to be located outside, one (1) foot above the highest sprinkler head, and no more than five (5) feet above grade at the installed location. 
  2. When the parameters for a PVB cannot be met, a Reduced Pressure-Principle (RP) - ASSE 1013 shall be installed. Required to be outside, no restriction on elevation of sprinkler heads, and mounted 18”- 24” above grade at the installed location.

PVB may be winterized in place; RP’s must be removed and placed in a warm storage area. Both assemblies require their annual test at the time of spring seasonal start-up.

Installation, repair, replacement and/or annual testing must be performed by a plumbing services firm (licensed plumber). Their plumbers must be at least of the “Journeyman” license level and also possess a separate cross connection technician certification. Do not be afraid to ask for proof!

Hint for owners with irrigation systems: make the testing part of your spring start-up contract. The irrigation firms may be able to procure the most favorable pricing due to their ability to deal in volume with plumbing services firms.

Fire Sprinkler Systems

Since their inception, residential fire sprinkler systems have been supplied with water by three different piping arrangements. The following describes the details of each variation:

  1. Dual Check Valve – This is the most common method of protection. The backflow devices are considered “non-testable” and the only required maintenance is rebuild or replacement of the device once every five years. A tag should always be hanging from the device identifying installation date, expiration date, or both.
  2. Passive Purge – Up to 2007, some homes were allowed to forego a physical backflow device in lieu of a system where stagnant water was purged from the system with usage of one or more toilets in the home. Typically, the water supply to one of the upper floor toilets was piped from the fire sprinkler system; upon each use, fresh water was introduced into the fire sprinkler system.

    If a dual check valve is not present, you can perform an easy test to verify if you have a passive purge system. Shut off the water supply to the home by operating the main valve above the meter and past the sprinkler system “take-off”. Then open the cold supply to a bathtub on the upper floor to ensure the water is off. Now flush each toilet, if connected to the normal water distribution piping, the tank will not refill. If connected to the fire sprinkler system, the toilet will refill despite the water being turned off to the rest of the home. This confirms the presence of a passive purge system. No backflow related maintenance is required, just be sure to continue using that specific toilet on a periodic basis to ensure fresh water is routed into the sprinkler system.
  3. “Testable” Double Check Valve Assemblies – Homes constructed from 2007 to 2009 were required (by code at that time), to install the testable version of a double check valve. Because the code has been relaxed since then, homeowners have two choices for maintenance and upkeep. Have the required testing done by a licensed plumber or replace the existing backflow assembly with a non-testable dual check valve and then rebuild or replace that device every five years.

Heating System / Boilers

Where water is connected to a heating system boiler as a make-up water supply, it must be protected by a dual check valve with integral vent (standard no. ASSE 1012). This device is considered “non-testable” and must be rebuilt or replaced every five years. If chemicals are added to the heating water system (this is not common), an ASSE 1013 must be installed and special provisions for drainage need to be considered and yearly testing by a plumber is mandatory.

Dark Room Sinks and Automatic Film Developers

Not a very common item for any household and with the advent of digital photograph, photo developers and sinks are certainly a rarity these days. But when connected to the water distribution system, backflow prevention is a must. If connected to a tank or sink, a “non-testable” device (standard no. ASSE 1012), may be utilized. If chemical injection is present or an automatic developer is used, a “testable” assembly (standard no. ASSE 1013), must be installed and special provisions for drainage need to be considered and yearly testing by a plumber is mandatory.

Other Water Uses

Consult with a licensed plumber regarding proper connection and protection requirements or contact a WSSC Water inspector by phone or email: 301-206-8886 or

Best Management Practices

Understanding and respecting the risk of water contamination is a great start, when in doubt, seek help. Basic guideline: every water outlet needs some form of protection; get to know what is needed.

Have “non-testable” backflow devices replaced at the intervals described above. Have “testable” backflow assemblies tested yearly and rebuilt or replaced as needed.

Last Modified: December 8, 2023, 8:22 am EST