What does a backflow prevention device do?
A backflow prevention device stops water from moving in the wrong direction through a plumbing system. Its purpose is to keep water that may contain soil, chemicals, fertilizer, cleaning products, or other contaminants from entering the drinking water supply.
Water distribution systems are designed to maintain pressure that pushes clean water toward homes and fixtures. Backflow becomes possible when that pressure changes or when another source creates greater pressure inside the plumbing. A properly selected and maintained device creates a barrier against that reverse movement.
The risk is not limited to commercial buildings. Residential plumbing can also contain cross-connections involving outdoor faucets, irrigation systems, hose-connected equipment, boilers, water treatment equipment, toilets, and utility sinks.
Why does backflow happen?
Backflow generally occurs through one of two hydraulic conditions: backsiphonage or backpressure.
Backsiphonage happens when pressure in the public water main drops below the pressure inside a connected plumbing system. This can occur during a water-main break, firefighting activity, heavy water use, or certain maintenance operations. The pressure change can act like suction, drawing water or another substance backward through a hose or pipe.
Backpressure occurs when pressure inside a private plumbing system becomes greater than the pressure in the supply line. Pumps, elevated tanks, boilers, solar heating equipment, and some water treatment systems can create this condition.
For example, a garden hose left in a bucket of lawn treatment solution can become a cross-connection. If water pressure drops while the hose is submerged, the liquid could be pulled into the household plumbing unless an appropriate protective device or air gap prevents it.
What is a cross-connection?
A cross-connection is any actual or potential connection between drinking water plumbing and a source that could contain unwanted material. The connection may be obvious, such as a hose submerged in a pool, or less noticeable, such as an improperly arranged appliance connection.
Common residential examples include:
- A hose lying in a swimming pool, laundry tub, rain barrel, or container of chemicals
- An underground lawn irrigation system connected to the household water supply
- A boiler or hydronic heating system
- A water softener or other treatment equipment
- A utility sink with a hose or spray attachment
- A toilet tank without adequate separation between the water supply and tank water
- A basement or crawl-space plumbing modification that was installed without required protection
A cross-connection does not automatically mean contamination has occurred. It means a pathway exists through which contamination could occur if water pressure changes.
How does a backflow preventer work?
Most devices use one or more check valves, springs, pressure-sensing chambers, or physical air gaps to control the direction of flow.
A check valve opens when water moves in the intended direction. If water tries to reverse direction, the valve closes against a seat to block the flow. Some assemblies use two check valves so that one provides backup protection if the other becomes fouled or fails.
A reduced pressure principle assembly, often used where the potential hazard is higher, contains two check valves and a relief zone between them. The relief valve is designed to open and discharge water if pressure conditions become unsafe. This arrangement helps prevent contaminated water from being pushed or pulled into the drinking water supply.
A pressure vacuum breaker uses a check valve and an air-inlet valve. It is commonly associated with irrigation or other connections where backsiphonage is the primary concern. The device must be installed in the correct position and location to work properly.
A hose-bib vacuum breaker is a smaller protective device installed on an outdoor faucet. It helps prevent water from being siphoned backward through a connected hose. It does not replace every type of backflow protection, particularly where backpressure or a higher hazard is present.
An air gap protects water by leaving a physical separation between the water outlet and the receiving vessel. This is one of the simplest forms of backflow protection. A faucet discharging above a sink basin, rather than below the waterline, is a familiar example.
Why does device selection matter?
The correct device depends on the type of cross-connection, the direction and strength of possible flow, the degree of hazard, and the installation conditions.
A device intended only for backsiphonage may not protect against backpressure. A simple hose-bib vacuum breaker may be suitable for one outdoor faucet but inadequate for an irrigation system with chemical injection. Likewise, a device installed backward, below the required elevation, or without access for testing may not provide the protection expected.
Michigan’s cross-connection control requirements work together with plumbing-code provisions. Public water systems may inspect plumbing arrangements, require corrective action, and establish testing schedules for testable assemblies. The protection method should match the actual risk rather than relying on a one-size-fits-all part.
What maintenance do these devices need?
Backflow preventers are mechanical devices, so they can become worn, clogged, corroded, or damaged by freezing. Dirt, mineral deposits, insects, and changes made to nearby plumbing can also affect operation.
Residents can reduce risk by:
- Disconnecting garden hoses after use, especially before freezing weather
- Avoiding submerged hose connections
- Protecting exterior faucets and assemblies from freezing
- Keeping access areas clear around testable devices
- Watching for unexplained discharge from a relief valve
- Reporting leaks or unusual pressure changes rather than blocking or capping a relief outlet
- Keeping records when a device is tested, repaired, or replaced
A device that leaks from a relief opening may be responding to a pressure condition, a fouled valve, or a damaged component. The discharge should not be ignored, but the relief path should not be sealed because it is part of the device’s safety function.
Are backflow preventers tested or inspected in Waterford?
Waterford’s cross-connection control program includes inspection of residential and commercial accounts. Some testable backflow assemblies require periodic testing by an appropriately certified tester, with the schedule depending on the property type and the local program.
For residential properties, inspection and testing are not always the same thing. A visual inspection checks whether a cross-connection exists and whether the installation appears properly protected. A performance test checks whether the internal valves and pressure relationships operate within required limits.
Not every household device is testable in the same way. A small hose-faucet vacuum breaker may be inspected for proper installation and condition, while a larger assembly serving irrigation or commercial equipment may require documented performance testing.
Property owners should read notices from the local water system carefully. Requirements can differ based on the assembly, the plumbing use, and the level of hazard. Testing of regulated assemblies must follow applicable Michigan qualifications and plumbing requirements.
What should residents check before using a hose or irrigation system?
A few habits prevent many common cross-connection problems:
1. Keep hoses out of pools, buckets, tubs, chemical containers, and pet-water vessels.
2. Use an approved vacuum-breaker device where required for exterior hose connections.
3. Make sure irrigation systems have the protection specified for their design.
4. Do not alter, bypass, remove, or cover a backflow assembly.
5. Before spring irrigation use, inspect for freezing damage, leaks, damaged shutoff valves, or missing test ports.
6. If plumbing has been remodeled, verify that new fixtures and equipment did not create an unprotected connection.
Seasonal freeze-and-thaw conditions in Michigan can damage outdoor plumbing and leave small valves unreliable when irrigation and hose use resume. A device that worked properly last season should still be checked after winter.
Backflow prevention does not improve taste, pressure, or water temperature. Its job is narrower and essential: keeping potentially unsafe water from reversing into the drinking water system.