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1. What is Backflow?

Backflow is the reverse flow of water caused by a loss of pressure in the system or connections to the system that have a higher pressure than the supply pressure.

2. What is back-siphonage?

Back-siphonage is the reversal of normal flow in a system caused by a negative pressure (vacuum or partial vacuum) in the supply piping.

3. What factors can cause back-siphonage?

Back-siphonage can be created when there is stoppage of the water supply due to nearby fire-fighting, repairs or breaks in city main, etc. The effect is similar to the sipping of an ice cream soda by inhaling through a straw, which induces a flow in the opposite direction.

4. What factors can cause a back pressure-backflow condition?

Back pressure-backflow is created whenever the downstream pressure exceeds the supply pressure, which is possible in installations such as heating systems, elevated tanks, and pressure-producing systems. An example would be a hot water space-heating boiler operating under 15-20 pounds of pressure coinciding with a reduction of the city water supply below this pressure (or higher in most commercial boilers). As water tends to flow in the direction of least resistance, a back pressure-backflow condition would be created and the contaminated boiler water would flow into the potable water supply.

5. What is a cross connection?

A cross connection is a direct arrangement of a piping line allowing the potable water supply to be connected to a line that contains a contaminant. An example is the common garden hose attached to a sill cock and the end of the hose is lying in a cesspool. Other examples are a garden hose attached to a service sink with the end of the hose submerged in a tub full of detergent, supply lines connected to bottom-fed tanks, supply lines to boilers.

6. What is the most common form of a cross connection?

Ironically, the ordinary garden hose is the most common offender as it can be easily connected to the potable water supply and used for a variety of potentially dangerous applications.

7. How can you help prevent backflow conditions?

To view the ways to prevent backflow for residential and commercial and industrial properties, please view the

Prevent Backflow Conditions page.