Egg smell after installing filter

Egg smell present after installing a new water filter

Quick Answer:

If a rotten-egg odor appears right after installing a water filter, the likely causes are hydrogen sulfide already in the supply, bacteria colonizing the new cartridge, or a short chemical reaction between disinfectants and fresh media. Before assuming the cartridge is defective, bypass the new filter briefly and retest the odor to see whether the smell follows the filter or the plumbing.

Why This Happens

  • Hydrogen sulfide (H2S) in the source water smells like rotten eggs. A new filter can make that smell more noticeable by concentrating or releasing trapped gases.
  • Some filter media release small amounts of trapped compounds when first used, or react with chlorine or chloramine in the water to produce odor temporarily.
  • New cartridges can also be a growth site for bacteria if they sit wet or were not flushed fully after installation.
  • Water temperature and appliances change how odors present — see issues like Odor that worsens when heater runs and related installation scenarios such as Egg smell after backflow install for similar patterns that help diagnose source.

Step-by-Step What to Do

Step 1 — Confirm where the smell is strongest

  • Check cold versus hot water at the nearest faucet and at a distant faucet. Note whether the odor is present only on hot, only on cold, or both.
  • Smell at the filter housing outlet and at a separate tap before the filter (if available).

Step 2 — Bypass the new filter and retest

  • Temporarily switch the plumbing around the filter or use the bypass valve so water flows without passing through the new cartridge.
  • Run water for a minute and smell again. If the odor disappears on bypass, the cartridge or housing is likely involved. If the odor remains, the source is upstream of the filter.

Step 3 — Flush the cartridge and housing

  • If the filter is new, follow the manufacturer’s recommended flush time (often several minutes to an hour of running water). This clears trapped air, dust, and loose media fines.
  • Run both cold and hot taps if the system serves both.

Step 4 — Inspect the installation

  • Check that the cartridge type is correct for your system and that seals and O-rings are seated properly.
  • Look for standing water in the housing or signs of bypass leaks that could allow untreated water to mix with treated flow.

Step 5 — Test by isolation

  • If possible, remove and cap the filter housing so you can compare water from the main supply line with and without the filter inline.
  • Consider running a faucet aerator-free for a direct sample.

Step 6 — Decide next steps based on results

  • If the smell stopped on bypass: keep the cartridge but consider further flushing, replacing the cartridge with the same brand (if it was new and possibly off-gassing), or swapping to a different media type after consulting the manufacturer.
  • If the smell continued on bypass: schedule testing of the source water and inspect upstream devices (heater, well components, backflow assemblies).

What Not to Do

  • Do not discard filters until reaction is proven — premature disposal wastes parts and removes a useful sample for diagnosis.
  • Do not pour strong household chemicals into the filter housing to “neutralize” odors; this can damage the system and create hazardous byproducts.
  • Do not assume the cartridge is dangerous without testing; many smells are nuisance odors rather than health hazards.

When to Call a Professional

  • The odor persists after you bypass and flush the system.
  • Multiple fixtures show the same smell, or the smell is strong and persistent.
  • Household members experience nausea, headaches, or other symptoms after using the water.
  • You detect signs of contamination at the well, or suspect a failed backflow device or heater issue you cannot isolate.

Safety Notes

  • A weak rotten-egg smell is usually hydrogen sulfide at low concentrations and is unpleasant rather than acutely dangerous, but strong concentrations can be hazardous — avoid prolonged inhalation.
  • If the smell is very strong, use bottled water for drinking and cooking until you know the source.
  • Wear gloves when handling cartridges and avoid directly tasting water to test odor; use short, cautious sniffs instead.
  • Keep records: do not throw away the cartridge before a professional or manufacturer inspects it if requested.

Common Homeowner Questions

  • Is the smell dangerous?
    Usually not at low levels, but avoid drinking strongly odorous water and seek testing if the smell is persistent.
  • Will flushing solve it?
    Often a thorough flush clears manufacturing residues or trapped gases within hours, but retest after bypass to be sure.
  • Should I remove the cartridge now?
    No — only remove it after confirming the cartridge is the source or if a professional or manufacturer recommends replacement.

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

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