5 Common Causes of Water Backflow & Ways to Prevent Them

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1. Backpressure from High Water Demand

Cause:

Backpressure occurs when the pressure in a non-potable water system exceeds the pressure in the clean water supply. This is common in commercial settings with boilers, pumps, or irrigation systems that create excessive water pressure.

Example: In a building with a high-pressure boiler system, if the boiler pressure exceeds the incoming municipal water pressure, backflow can occur, pushing boiler water (potentially containing chemicals) into the drinking water supply.

Prevention:

• Install a Reduced Pressure Zone (RPZ) Backflow Preventer: RPZ valves are considered the most reliable type of backflow prevention. They use two independently operating check valves and a pressure differential relief valve to maintain a lower pressure zone between the potable and non-potable systems, ensuring backflow is virtually impossible.

• Regularly Inspect and Maintain Boilers and Pumps: Schedule routine inspections (every 3-6 months) to check for pressure imbalances and ensure equipment is functioning correctly.

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2. Backsiphonage Due to Sudden Pressure Drops

Cause:

A sudden drop in water pressure can create a vacuum that pulls contaminants into the potable water system. This can occur during fire hydrant usage, water main breaks, or high-demand periods.

Example: If a fire hydrant is opened nearby, it can cause a significant drop in water pressure in the surrounding area. This vacuum can pull water from a garden hose connected to a faucet, potentially siphoning pesticides or fertilizers back into the household water supply.

Prevention:

• Use a Vacuum Breaker: Install atmospheric vacuum breakers (AVBs) or pressure vacuum breakers (PVBs) on all faucets and hose connections. These devices allow air to enter the pipe when a vacuum occurs, preventing the back-siphoning of contaminated water.
• Routine Municipal Water System Checks: Municipalities should conduct regular checks and maintenance of water mains to minimize the risk of sudden pressure drops.
  

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3. Faulty or Worn-Out Backflow Preventer Valves

Cause:

Backflow preventer valves can degrade over time, leading to leaks and malfunctioning seals. If these valves fail, contaminated water can mix with the clean water supply.

Example: A check valve in a backflow preventer may become corroded or stuck in the open position, allowing backflow to occur during a backpressure or backsiphonage event.

Prevention:

• Annual Backflow Testing: As mandated in Mississauga and the GTA, conduct annual backflow testing by a certified technician. Testing ensures that the valves are functioning correctly and meet local regulatory requirements.
• Regular Valve Replacement: Replace check valves, pressure relief valves, and seals every 5-7 years, or as recommended by a certified technician, to prevent failures due to wear and tear.
  

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4. Cross-Connections in Plumbing Systems

Cause:

A cross-connection occurs when clean and contaminated water sources mix due to improper plumbing installations. This often happens in garden hoses, sprinkler systems, and dishwashers connected without proper backflow prevention.

Example: Connecting a garden hose to a chemical tank or a laundry tub without proper backflow prevention creates a cross-connection. If the pressure drops, chemicals or dirty water can be siphoned back into the household water supply.

Prevention:

• Use Hose Bib Vacuum Breakers: Install hose bib vacuum breakers on all outdoor faucets and hose connections to prevent back-siphonage.
• Proper Air Gaps: Ensure proper air gaps (at least twice the diameter of the water supply inlet) in dishwashers, sinks, and irrigation systems to prevent backflow.
• Professional Plumbing Installations: Always hire licensed and experienced plumbers for any plumbing installations or modifications to ensure compliance with local codes and regulations.
  

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5. Submerged or Contaminated Water Sources

Cause:

If a garden hose or water outlet is submerged in dirty water, chemicals, or sewage, contaminants can be drawn into the clean water system when pressure changes occur.

Example: Leaving a garden hose submerged in a swimming pool or a bucket of soapy water can create a backflow hazard if the water pressure drops. The contaminated water can be siphoned back into the household water supply.

Prevention:

• Never Submerge Hoses: Avoid submerging hoses in pools, buckets, chemical tanks, or any potentially contaminated water source.
• Install Backflow Prevention Devices: Install backflow prevention devices on all irrigation and outdoor plumbing connections to prevent contamination from submerged sources.
  

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Backflow Prevention Devices: Choosing the Right Solution

Selecting the correct backflow prevention device depends on the level of hazard and the specific application. Here’s a brief overview of common types:

• Atmospheric Vacuum Breaker (AVB): Simple and cost-effective, suitable for low-hazard applications like irrigation systems and hose bibs. Must be installed at least 6 inches above the highest point in the system.

• Pressure Vacuum Breaker (PVB): More reliable than AVBs, suitable for moderate-hazard applications like sprinkler systems. Must be installed above the highest point in the system.

• Double Check Valve Assembly (DCVA): Consists of two spring-loaded check valves. Suitable for low to moderate-hazard applications like fire sprinkler systems and commercial dishwashers.

• Reduced Pressure Zone (RPZ) Backflow Preventer: Offers the highest level of protection, ideal for high-hazard applications like hospitals, chemical plants, and boiler systems. Features two check valves and a pressure relief valve.

Local Regulations and Compliance in Mississauga & GTA

In Mississauga and the GTA, backflow prevention is regulated to safeguard public health. Key regulations include:

• Annual Testing: All backflow prevention devices must be tested annually by a certified technician.

• Device Certification: Backflow preventers must be certified to meet specific standards (e.g., CSA, ASSE).

• Permitting: Installation and replacement of backflow preventers may require permits from the local municipality.

Compliance with these regulations is crucial to avoid penalties and ensure the safety of your water supply. For specific regulations and requirements in your area, consult your local municipality’s website or contact a certified plumbing professional.

Sources

• https://www.mississauga.ca/services-and-programs/building-and-renovating/building-permits/drawings-and-documents-you-need-for-a-building-permit/backflow-preventer/
• https://www.toronto.ca/services-payments/water-environment/water-sewer-related-permits-and-bylaws/water-supply-by-law/backflow-prevention-program/

Protect Your Water Supply with Regular Backflow Prevention

Regular maintenance, proper device selection, and compliance with local regulations are essential for effective backflow prevention. To ensure your backflow prevention system is functioning correctly and protecting your water supply:

• Schedule Annual Backflow Testing: Contact a certified technician for annual testing and inspection.

• Replace Worn Valves and Seals: Replace worn components to prevent leaks and failures.

• Ensure Proper Installation: Have backflow preventers installed by licensed plumbers in mississauga to ensure compliance with local codes.

If you’re in Mississauga or the GTA, ensure your system is compliant with local regulations to safeguard your home or business from contaminated water.

Regular maintenance and timely valve replacements can prevent costly repairs and ensure your water remains safe.

📞 Call Select Plumbing and Heating for professional Water backflow prevention, repair and installation.