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.
What Can Cause a Backflow
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.
Additional Protection Needed
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.
Types of Backflow Preventers
There are two basic types of backflow preventers: testable and non-testable.
Testable Backflow Preventers
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.
Non-Testable Backflow Preventers
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.
Application of Backflow Preventers
the following is a quick view of applications that require either a testable or non-testable backflow preventer.
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