Egg smell after backflow install

Egg smell after installing a backflow preventer

Quick Answer:

If you notice an egg-like (rotten) smell after having a backflow device installed, it’s usually not a chemical change to the public supply. A new device can change flow, create pockets of stagnant water, or disturb bacteria in your pipes that release hydrogen sulfide gas. Start by flushing lines and checking the backflow device orientation, then retest system pressure. If the smell continues, call a plumber for testing and possible disinfection.

Why This Happens

  • Hydrogen sulfide (the “rotten egg” smell) is often produced by bacteria in stagnant water inside pipes or fixtures. Changing pipe flow or creating new dead-legs can release that odor.
  • Installing a backflow preventer can alter pressure and flow patterns. That may mobilize trapped water or sediments that had been odor-free until disturbed.
  • Similar smells can come from hot water equipment. If the heater or its anode was disturbed recently, see Rotten smell after water heater replacement for how that can behave.
  • Timing of the smell gives clues. If it appears only on the first draw from a tap after sitting, that points to standing water in the immediate plumbing rather than the public supply.

Step-by-Step What to Do

1. Confirm where and when the smell appears

  • Check multiple taps: cold vs hot, kitchen vs outside hose, upstairs vs downstairs.
  • If the odor is strongest on the first use after several hours of no flow, it’s likely local standing water—see Odor only in first water draw.

2. Flush the affected lines

  • Run the cold tap for 5–10 minutes and then the hot tap for 5–10 minutes. Open kitchen faucet, shower, and an outdoor hose bib to move water through the system.
  • Remove and clean faucet aerators and showerheads; trapped debris there often holds odors.

3. Inspect the backflow device orientation

  • Visually check that the backflow preventer is installed upright and according to the manufacturer’s markings (inlet/outlet arrows and orientation marks).
  • Look for trapped pockets or low points where water could stagnate just upstream or downstream of the device.
  • If anything looks loose, leaking, or improperly mounted, stop and note what you see for a professional—do not try to reposition internal parts yourself.

4. Retest system pressure

  • Measure static and working pressure at an outdoor hose bib with a simple pressure gauge if you have one: record the numbers before and after running water and after any adjustments.
  • Compare pressure readings to typical household values (usually 40–60 psi). Significant drops or unusual fluctuations after installation can indicate installation issues that affect flow and odor.
  • If you don’t have a gauge, a plumber can quickly test and record pressures for you.

5. Check the water heater and storage sections

  • Run hot water separately; if the smell is only in hot water, the heater could be the source. Flushing the heater or replacing the anode may help.
  • If you recently had water heater work done, that can disturb bacteria or sediments—refer to the guidance above for heater-related odors.

6. If flushing and checks don’t work, arrange testing

  • Have the water tested for hydrogen sulfide and bacterial counts. Your local health department or a licensed lab can advise on sampling.
  • If tests show contamination or persistent bacteria, a plumber can perform shock chlorination or other treatments safely.

What Not to Do

  • Do not reverse backflow devices to fix smell. Reversing or reorienting the device yourself can break the unit, violate code, and create a health hazard.
  • Do not pour large amounts of bleach down fixtures without guidance; improper disinfection can corrode plumbing or create unsafe byproducts.
  • Do not dismantle the backflow preventer unless you are certified and familiar with local backflow testing requirements—these devices are often regulated and must be re-tested after service.

When to Call a Professional

  • If the odor returns after flushing and pressure retests, or if only one part of the house smells despite flushing.
  • If pressure readings are abnormal after installation, if the backflow device looks misinstalled, or if the device leaks.
  • If water testing shows hydrogen sulfide or bacterial contamination, or if anyone in the home becomes ill or has sensitivities.

Safety Notes

  • Do not drink or cook with water that smells strongly of eggs until you are confident it is safe. Use bottled water if you have concerns.
  • Avoid home chemical treatments unless advised by a professional; wrong chemicals or dosages can damage plumbing and create hazards.
  • Backflow preventers are safety devices. Any repair or replacement may trigger local testing or certification requirements—hire a licensed plumber familiar with those rules.

Common Homeowner Questions

  • Why does the smell come back after I flush? If bacteria are in a section of pipe or the water heater, short flushing may not remove them; professional disinfection may be needed.
  • Can a backflow device let contaminants into my house? If installed correctly and functioning, it prevents cross-connections. Incorrect installation or damage can reduce effectiveness—have it inspected.
  • Is the public supply likely the problem? It’s uncommon; most rotten-egg smells originate in household plumbing or water heaters. Testing will confirm the source.

For more related articles, see the Sulfur / Rotten Egg Smell in Water hub.

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