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Backflow Cross-Connection Testing

What is a Cross-Connection?

A cross-connection is a point in a plumbing system where the potable (drinking) water supply is or can be connected to a non-potable source (water not intended for drinking). There are two types of cross-connections, direct and indirect. A Direct Cross-Connection is a connection on a potable water system by a non-potable pressurized line such as irrigation lines, boiler lines, chemical transfer lines, etc. An Indirect Cross-Connection is a connection on a potable water system by a line, or hose, and is usually open at one end. Examples of Indirect Cross-Connections are garden hoses, sprinkler systems, water softeners, bathtubs, showers, wash basins, etc. Some examples of Indirect Cross-Connections made with a garden hose are:

  • A garden hose attached to a pesticide/chemical spray bottle.
  • A garden hose filling a pool with the downstream end of the hose being submerged by the non-potable water.

What is a Backflow?

“Backflow” means the undesirable reversal of flow of water. This is through a cross connection into the public water system or consumer’s potable water system.

Backflow is the flow of water (or other solid, liquid, or gas from any source) back into the potable water supply. Backflow may be due to either: Backsiphonage; or Backpressure.

“Backsiphonage” means backflow due to a reduction in system pressure in the purveyor’s distribution system and/or consumer’s water system. “Backpressure” means a pressure (caused by a pump, elevated tank or piping, boiler, or other means) on the consumer’s side of the service connection that is greater than the pressure provided by the public water system and which may cause backflow.

Example of a Cause of Backflow - Backsiphonage

Backsiphonage is backflow caused by negative pressure in the water supply piping. This occurs when system pressure is reduced below atmospheric pressure. The effect is similar to sipping water through a straw.

The following scenario illustrates how back siphonage backflow conditions could occur in a public water system:

  • A public water system main is shut off to repair a leak. The water main is at the base of a hill.
  • The water main is at a lower elevation than the homes on the hill. This creates a situation where water in the plumbing in the homes on the hill can drain into the public water system main.
  • When a customer at the bottom of the hill uses water, a siphon is created at households at the top of the hill and water drains out of their plumbing systems.
  • At one household at the top of the hill, a garden hose is being used to fill a child’s wading pool. The hose is submerged in the pool.
  • When the backflow conditions occur, the non-potable water from the wading pool is siphoned through the cross-connection (submerged hose) into the household plumbing and then into the water main.
  • The water from the wading pool contaminates the water main.
  • When water service is restored, contaminated water is delivered to customers served by the public water system.

Prevent Cross-Connections

Keep drinking water safe from contaminates is easy. Find and eliminate Cross-Connections. Install Backflow devices, assemblies, or air gaps. Install hose bib vacuum breakers on water fixtures. Something as useful as your garden hose has the potential to contaminate your home’s water supply. More than half of the nation’s Cross-Connections involve unprotected garden hoses.

Types of Backflow Prevention

Backflow can be prevented in two ways. Either through the installation of an air gap that provides a separation between the contaminated water and the drinking water or devices or assemblies that prevent the occurring backflow.