Backsiphonage: The Invisible Risk to Your Drinking Water
Published by Backflow USA
www.BackflowUSA.com
What Is Backsiphonage?
Backsiphonage is a dangerous form of backflow that occurs when the pressure in a water supply line drops below atmospheric pressure, creating a vacuum that pulls contaminants backward into the clean water system.
Think of it like sucking liquid through a straw—when negative pressure is introduced, whatever is connected to the line can be drawn in, including chemicals, bacteria, or non-potable water.
This hidden hazard is especially concerning in commercial irrigation, industrial processes, or even homes with hose attachments and sprinkler systems.
What Causes Backsiphonage?
Unlike backpressure, which results from excess force pushing backward, backsiphonage is caused by suction due to a sudden drop in supply pressure. This can happen in several common situations:
- Water Main Breaks: A broken city main or emergency shutoff can cause a sudden drop in municipal water pressure, creating a vacuum effect.
- Hydrant Flushing or Firefighting: When fire departments tap into hydrants, they pull water at high volumes, temporarily lowering nearby pressure and triggering backsiphonage from nearby properties.
- Elevated System Drain-Downs: If a tank, cooling tower, or high-elevation reservoir is drained quickly, the negative pressure it creates can siphon water (and contaminants) from lower plumbing fixtures.
- Hose or Sprinkler Connections: Unprotected garden hoses submerged in pools, chemical containers, or puddles can become pathways for contamination when suction is present.
Why Backsiphonage Is a Serious Threat
Backsiphonage is invisible. It happens silently—and often goes undetected until contamination has already occurred.
Key Dangers Include:
- Drinking Water Contamination: Pesticides, sewage, and industrial chemicals can be pulled into potable water lines.
- Health Code Violations: Local plumbing codes in the United States require backflow prevention devices specifically to protect against backsiphonage events.
- High Liability for Property Owners: If a backsiphonage incident contaminates shared or municipal lines, the property owner can face fines or legal action.
How to Prevent Backsiphonage in Your System
Prevention is not just smart—it’s required by law in many cities, especially for commercial and multi-unit properties.
✅ Recommended Prevention Measures:
- Install Vacuum Breakers or PVBs: A Pressure Vacuum Breaker (PVB) or Atmospheric Vacuum Breaker (AVB) protects against suction-based backflow.
- Use Hose Bib Anti-Siphon Valves: These inexpensive screw-on devices prevent garden hose contamination and are a must for homeowners.
- Maintain Air Gaps: Always maintain vertical air gaps between hose ends and any standing water or chemicals.
- Perform Annual Backflow Testing: Certified testing ensures your prevention devices are functional and compliant.
Backsiphonage vs. Backpressure: Know the Difference
| Type | Cause | Direction of Force | Risk Example |
|---|---|---|---|
| Backpressure | Excess downstream pressure | Pushes backward | Pressurized boiler pushing water into supply |
| Backsiphonage | Negative supply-side pressure | Pulls contaminants in | Fire hydrant use pulling irrigation water |
Protect Your Property from the Hidden Threat of Backsiphonage
Whether you’re managing a commercial property, maintaining an irrigation system, or simply trying to protect your home’s drinking water—backsiphonage is a risk you can’t afford to ignore.
Let Backflow Testers LLC help you:
- Identify vulnerabilities
- Install compliant vacuum breakers
- Conduct certified backflow testing
- File required reports with your local water district