What Is a Cross-Connection and How Does It Create Contamination Risk?

Definition

A cross-connection is any actual or potential physical connection between the public potable (drinking) water supply and any source of contamination or pollution. Cross-connections can be direct — a hose submerged in a bucket of chemicals — or indirect — a fire sprinkler system whose piping may contain antifreeze, rust inhibitors, or standing water of unknown quality.

How Cross-Connections Cause Contamination

Under normal conditions, water pressure in the public main is higher than pressure in connected systems, which keeps water flowing in one direction — from the main into the building. Cross-connections become hazardous when this pressure relationship reverses.

Back-siphonage scenario: A water main breaks nearby. Fire department crews hook up to hydrants. Demand exceeds supply. Pressure in the public main drops below the pressure in your building system. Any open connection between your system and the main acts as a siphon, pulling whatever is in your pipes back into the public water supply.

Backpressure scenario: A boiler system or pump raises pressure in your piping above the main pressure. If the connection between your system and the supply is unprotected, your high-pressure system pushes its contents into the public main.

Common Cross-Connections Found During Surveys

• Unprotected irrigation systems with fertilizer or pesticide injection
• Fire sprinkler systems connected directly to potable supply without a backflow preventer
• Chemical dispensing equipment with direct water connections
• Submerged inlets in sinks, tanks, or process vessels
• Boiler and hydronic heating systems connected to the potable supply
• Car wash equipment with detergent injection

The Solution

The solution to cross-connection hazard is proper backflow prevention: installing the appropriate type of backflow prevention assembly for the hazard level and maintaining it through annual testing. Eliminating the cross-connection entirely (by creating an air gap) is the best protection but is often not practical for operating systems.