What Causes Backflow to Occur?

Backflow is one of those hidden plumbing issues that can put your family, customers, or tenants at risk without you even realizing it. It happens when water flows in the reverse direction, potentially pulling contaminants into your drinking water lines.

As Atlas Backflow Services, we help property owners across L.A. understand the risks, prevent problems, and stay compliant. Below, our Backflow Testing Los Angeles technicians recommend practical steps and insights to keep your water safe.

What Is Backflow?

Backflow is the unwanted reversal of water flow in your plumbing system. Instead of clean water moving from the public supply into your property, it’s forced backward—bringing pollutants or contaminants along for the ride.

This is especially dangerous when there are cross-connections—places where potable water can come into contact with non-potable sources (like irrigation lines, boilers, or chemical feed systems).There are two primary causes of backflow: back-siphonage and backpressure.

Back-Siphonage: Negative Pressure Pulls Water Backward

Back-siphonage occurs when there’s a drop in pressure in the supply line. Think of sipping through a straw—negative pressure creates suction. In plumbing, this can happen when:

• Water main breaks or hydrant use: A nearby main break or heavy hydrant draw for firefighting can create a temporary vacuum. That sudden negative pressure can siphon contaminated water from your property’s system into the public supply.

• Pump failures: If booster pumps fail or a large fixture rapidly draws water, the pressure drop can trigger back-siphonage.

• Elevated fixtures: Tall buildings or rooftop systems can experience siphon effects when elevation changes are combined with pressure dips.

Our Backflow Testing Los Angeles technicians recommend having air gaps or appropriate backflow assemblies on irrigation, hose bibs with chemical attachments, lab faucets, and anywhere you could connect a hose to a chemical or fertilizer source.

Backpressure: When Your System Pushes Against the Supply

Backpressure happens when the pressure inside your building’s system exceeds the pressure in the supply line. Picture a boiler or closed-loop system building more pressure than the city main—water then forces its way backward.

Common causes include:

• Boilers and closed heating systems: Thermal expansion increases pressure. Without a working expansion tank and relief valves, it can push water back.

• Commercial equipment: Carbonators for beverage systems, industrial pumps, and process equipment often create higher internal pressures.

• Improperly set or failing pressure regulators: If your PRV is faulty, internal pressures can spike, especially during low municipal pressure events.

To mitigate this, our Backflow Testing Los Angeles technicians recommend verified expansion tanks on hot water systems, proper pressure regulating valves, and the correct backflow prevention assembly for the hazard level.

Where Backflow Risks Hide

Backflow risks appear wherever clean water meets a potential contaminant. Key hotspots include:

• Irrigation systems: Fertilizer injectors and standing water in sprinkler lines are notorious cross-connection risks.

• Hose connections: Garden hoses dunked in buckets, pools, or connected to sprayers can create direct contamination routes.

• Commercial kitchens: Dishwashers, pre-rinse units, and carbonated beverage systems need proper protection.

• Medical, dental, and lab facilities: Sterilizers, aspirators, and specialized equipment often require high-hazard protection.

• Fire sprinkler systems: Anti-freeze loops and stagnant water sections must be isolated with proper assemblies.

• Boilers and cooling towers: Chemical treatment and thermal expansion make them high risk without RP-type protection.

Our Backflow Testing Los Angeles technicians recommend a comprehensive cross-connection survey to identify and prioritize these risks—especially if your site has been remodeled or equipment has been added over time.

The Assemblies That Keep You Safe

Choosing the right backflow prevention assembly depends on your hazard level and application:

• Air Gap: The gold standard—physical separation between water outlet and the flood level rim. No moving parts; ideal for the highest hazards at point-of-use.

• Atmospheric/Vented Vacuum Breakers (AVB/SVB): Great for back-siphonage on irrigation and hose bibs, but not for continuous pressure or backpressure.

• Pressure Vacuum Breaker (PVB): Common on irrigation systems; protects against back-siphonage under continuous pressure.

• Double Check Valve Assembly (DC or DCVA): Suitable for low hazard (non-health) scenarios; protects against back-siphonage and backpressure.

• Reduced Pressure Principle Assembly (RP or RPZ): The most robust mechanical option for health hazards; handles both back-siphonage and backpressure with a relief valve.

Our Backflow Testing Los Angeles technicians recommend RP assemblies for high-hazard applications (like chemical feeds, carbonators, and medical equipment), PVBs or SVBs for many irrigation systems, and DCVAs for low-hazard services as allowed by code.

Signs You Might Have a Backflow Problem

While testing is the only reliable way to know your assembly is working, watch for:

• Sudden pressure changes or sputtering faucets

• Discolored water, unusual taste, or odors

• Air in lines after hydrant use or main breaks nearby

• Irrigation zones not holding pressure or water pooling at backflow boxes

• Boiler relief valve discharges or expansion tank failures

If you notice any of these, our Backflow Testing Los Angeles technicians recommend immediate evaluation and testing to protect your water quality.

Compliance in Los Angeles

In most jurisdictions—including Los Angeles—backflow prevention assemblies must be:

• Correctly selected for the hazard

• Professionally installed with proper clearances and drainage

• Tested at least annually by certified testers, and after installation, relocation, or repair

Municipal water providers typically require test reports and may issue notices for overdue assemblies. Staying proactive prevents fines and, more importantly, keeps contaminants out of the public water system.

How to Prevent Backflow: Best Practices

To minimize your risk year-round:

• Identify cross-connections: Conduct or schedule a site survey.

• Install the right assemblies: Match device type to hazard level and application.

• Test annually: Valves and springs wear; only certified testing proves performance.

• Maintain pressure balance: Verify PRVs and booster pumps are set correctly.

• Manage thermal expansion: Use properly sized expansion tanks on water heaters and boilers.

• Use air gaps where possible: Especially at chemical mixing and janitorial stations.

• Protect irrigation systems: Keep vacuum breakers above downstream piping and away from flood hazards.

• Plan for emergencies: After a main break, hydrant use, or construction event, schedule a check.

Our Backflow Testing Los Angeles technicians recommend syncing your annual test with seasonal milestones (like pre-summer irrigation start-up) and any time you modify plumbing or add equipment.

Why Choose Atlas Backflow Services

Atlas Backflow Services specializes in backflow testing, repairs, replacements, and compliance reporting for homes, businesses, and multi-unit properties across Los Angeles. Here’s what you can expect:

• Certified testing and clear reports submitted per local requirements

• Expert device selection for your exact hazard and code requirements

• Efficient repairs and replacements with stocked parts and minimal downtime

• Reminder scheduling so you never miss your annual test window

When safety, compliance, and reliability matter, our Backflow Testing Los Angeles technicians recommend getting ahead of the problem before it starts.

Final Takeaway

Backflow occurs due to back-siphonage (pressure drops creating suction) and backpressure (your system pushing against the supply). It’s driven by real-world events—main breaks, hydrant flows, failing PRVs, boilers, pumps, and everyday cross-connections like irrigation and hose bibs.

The fix is straightforward: choose the right backflow prevention assemblies, maintain your system, and test annually.Need help today? Contact Atlas Backflow Services to schedule the thorough, compliant testing and protection our Backflow Testing Los Angeles technicians recommend. Protect your water, protect your property, and keep Los Angeles’ water supply safe for everyone.