The following is presented to provide a general explanation on the subject of backflow prevention. It is not intended to be used in place of Code requirements and professionals should always utilize the code when making design, installation, and/or maintenance decisions. Definitions of italicized words follow at the end.
When drinking water piping connects to various plumbing fixtures or water utilizing equipment a cross-connection is created. If improperly protected, contamination can result when a backflow event occurs; allowing contaminates to reverse flow from the fixture/equipment back into the drinking water piping.
Conditions that are likely to create a backflow event are typically common, but unfavorable, hydraulic events that occur within the public or private segments of the water distribution system such as: an owner or worker draining down a house or building to make a plumbing repair; a broken water main or distribution pipe; severe/widespread power outages; fire fighters using large quantities of water to extinguish a fire, or; a water utilizing piece of equipment or process creating pressures greater than those present in water distribution system.
When these unfavorable hydraulic events are occurring, contaminates can be back-siphoned into the drinking water due to negative pressures; or contaminates can back-pressured into the drinking water due to excessive pressure imposed by the water utilizing piece of equipment or process.
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 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.
So around the home and office, for the most part, standard plumbing fixtures do not present a hazardous condition. However, additional protections are needed for household items such as: hand held shower heads; hose bibbs; lawn irrigation; and boilers.
In addition to the few items around the home that require additional protection, there are numerous applications within commercial and industrial processes that require additional protection. In general, these applications cannot utilize the air gap method of protection because the equipment or process requires a direct connection in order to utilize the dynamic pressure and flow that already exists within the water distribution system.
Therefore, directly connected water piping requires a different method of protection; the backflow preventer. A backflow preventeris a “one-way” appurtenance (an assembly of check valves or a vacuum breaker), that only allows water to flow in the desired direction and physically impedes reverse flow.
There are two basic types of backflow preventers: testable and non-testable.
also referred to as Backflow Prevention Assemblies; Backflow Assemblies; Testable Assemblies; or simply, Assemblies. Backflow Prevention Assemblies are generally required on the more hazardous cross connection applications, see below. By federal, state and local requirements as well as the manufacturer’s product listing, annual testing is required to ensure the assembly is good working order. This is due in part because the working components of a backflow assembly have a fairly short life expectancy and/or because sediment and debris can easily block their proper function.
When required testing fails to produce satisfactory results, assemblies must be cleaned and/or rebuilt as needed and retested. Un-repairable or obsolete assemblies must be replaced. See more below, for reporting, permitting, and licensing requirements.
also referred to as Backflow Prevention Devices; Backflow Devices; Non-Testable Devices; or simply Devices. Backflow Prevention Devices are generally required on the less hazardous cross-connection applications, see below. Some devices are required to be replaced every five years; while others are good for the life of the fixture they serve or until they visibly fail (leak externally). See below.
the following is a quick view of applications that require either a testable or non-testable backflow preventer. For a comprehensive look at selection criteria please visit Table 5.1 in the WSSC Plumbing and Fuel Gas Code. In fact, take a look at Chapter 5 in its entirety; it is all about Cross-Connection Control.
Irrigation, in ground (All Homes & Businesses)
Commercial Water Treatment
Vehicle Washing Facilities
Commercial Fire Sprinklers
Residential Hose Bibbs
Hand Held Shower Heads
Emergency Eye Wash
Residential Fire Sprinkler
Commercial Ice Makers
Food Service Equipment
ASSE 1012 – Dual Check Valve; with Atmospheric Vent
ASSE 1022 – Dual Check Valve; with Atmospheric Vent for Carbonated Beverage Dispenser
ASSE 1024 – Dual Check Valve
These devices require tagging to identify the installation and/or expiration date. Homeowners can replace these devices without permit or inspection.
also referred to as Backflow Technician; Backflow Tester; or simply, Tester. By Maryland Law, and subsequently by WSSC Plumbing Code, Backflow Techs must be registered as, at minimum, a Journeyman Plumber and also have completed a State of MD sanctioned 40 hour certification course for Cross-Connection Technicians ( and re-cert every 3 years).
under Maryland Law, only firms registered under a licensed Master Plumber can perform Plumbing Services which includes the installation, repair and testing of backflow prevention assemblies.
Therefore, cross-connection technicians have to be performing their duties under the direction of a registered plumbing services firm.
the following link is a list of licensed plumbing firms who have declared they provide this specialty line of services. WSSC has validated their licensing credentials, but does not endorse these firms; you are free to choose any licensed firm.
numbered forms can only be purchased by registered plumbing services firms. Upon completion of a test on a testable assembly, registered cross-connection technicians are required to electronically submit their reports, to WSSC, within 5 business days.
the “first time” installation of a new testable backflow assembly or relocation of an existing testable assembly requires a long form permit and inspection.
the replacement of an existing backflow assembly, in kind and location, requires a short form permit and inspection.
testing of backflow assemblies shall be performed in the spring when system start-up/reactivation occurs. This typically applies to irrigation systems, pools, pool houses, summer/beach houses, campgrounds, park restrooms, amusement rides, etc. WSSC is systematically resetting all annual test due dates to May 1. Note: testing is only required once per year, but from this point forward, it should be done in the spring, before May 1.
Rationale: Backflow assemblies that have been de-pressurized, removed or winterized in-place are at the greatest risk of failure because they were subjected to “no-flow”, “no-pressure” conditions. Like most mechanical devices, lack of movement is bad on the working parts, not to mention the affect dried residue and/or nesting bugs can have on them as well.
Hint for owners: for pools and irrigation systems, make the testing part of your spring start-up contract. The pool and irrigation firms may be able to procure the most favorable pricing due to the ability to deal in volume with plumbing services firms.
Industry experts recognize that WSSC Code Officials (Plan Reviewers and Inspectors), Design Engineers, Plumbing Installers and knowledgeable owners have done an exceptional job to ensure that the right form of backflow protection was specified, approved, and installed, over recent decades, for tens of thousands of cross-connections. However, perpetual maintenance is equally as important.
federal, state and underwriting authorities mandate that water purveyors, like WSSC, follow-up on cross-connections and backflow prevention, in addition to initial construction efforts. Since 2010, WSSC has increased its efforts in this area.
WSSC began with its own treatment plants and pumping stations to ensure that we are in full compliance; we are. Then inspections commenced on a priority based matrix, where the highest priority was given to commercial properties, containing the highest degree of hazards, coupled with an assessment of their hydraulic vulnerability.
is responsible for inspecting existing buildings for un-protected or improperly protected cross-connections. WSSC currently has eight full time inspectors canvassing the service area on the established priority basis. The program also utilizes a strong administrative support staff to maintain our database, send reminder notices, and administer our self-survey program, more below.
WSSC maintains a database of annually tested backflow preventers. Information from electronically submitted test reports is directly uploaded to this database. In addition, the database can determine when backflow assemblies are out-of-date for testing and generate reminder notices.
WSSC needs your help to catch-up on years of non-reporting and a general lack of follow-up compliance (testing). To enhance the database and ensure follow-up compliance, WSSC is asking its commercial and industrial water customers to complete a self inspection or “self survey” of all connections to the water system within their property. Homeowners who have a testable backflow assembly are asked to self report as well; a simple call or email will do. See contact information below.
The self survey form may be completed by a knowledgeable representative of the owner or tenant or by a licensed plumber who has a current cross-connection certification. If you are a property or building owner, please have the survey completed for the backflow assemblies under your ownership and control. If you are a tenant or unit owner, please complete the survey for the backflow assemblies under your ownership and control. Please share this notice openly between ownership and tenants so the overall results will be all inclusive and accurate with respect to controlling entities.
When discovered, un-protected water uses, or protected outlets that are overdue for a test, must be corrected. Maryland State Plumbing Code, and subsequently WSSC’s Plumbing Code, requires the installation and testing of backflow prevention assemblies to be performed by licensed plumbers who also possess certification as a backflow technician.
Compliance may also help in reducing your liability. Note: if you are responsible for a cross-connection (whether un-protected, improperly protected, or out-of-date for service) and a backflow event occurs, you may be liable for the resultant sickness, death, or property damage.
Yes, it can be that serious.
by email at: InspectionSupport@wsscwater.com or by phone: 301-206-4004.
is the physical connection between the potable water system and an “end-use” where a potential hazard exists.
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 private water distribution system.
the un-obstructed vertical distance between a water outlet and the flood rim level of a potential source of contamination; the air gap shall not be less than twice the diameter of the water outlet and never less than one (1) inch.
water distribution piping connected, without an air gap, to an “end-use” where a potential source of contamination exist.
is a “one-way” appurtenance (an assembly of check valves or a vacuum breaker), that only allows water to flow in the desired direction and physically impedes reverse flow.
means to install, maintain, extend, alter, or remove piping, a plumbing fixture, a plumbing appliance, a plumbing appurtenance, or other plumbing apparatus within a building or on-property where such plumbing is connected to a public or private sewerage system or connected to a private or public water system.