Quick Answer:
If you notice an odor after installing a new water filter and testing the water, it’s often temporary. First check that the filter is installed inline and the bypass valve is fully closed, then flush the unit as the manufacturer recommends. Small trapped air pockets, open sanitary fittings or carbon packing can cause brief smells. If you recently turned the water back on, see Smell after turning water back on for related tips.
Why This Happens
- Trapped air pockets can concentrate odors and release them when water flows.
- New filters — especially those with activated carbon — can have packing dust or factory scents that clear after flushing.
- If a bypass valve was left open or the filter isn’t inline, untreated water can mix with treated flow and smell different.
- Open sanitary caps or exposed fittings can let dirt or packaging material enter the cartridge area during install.
Step-by-Step What to Do
Verify the filter is inline and the bypass valve is fully closed
Visually confirm the filter housing and tubing are installed in the main flow path, not around it. Check the bypass assembly: most valves have a clear “bypass” position and a “service” or “in-line” position. Turn the valve to the in-line/service position and verify water now flows through the cartridge.
Flush the filter per manufacturer instructions
Run water through the new filter for the exact time or number of gallons the manufacturer specifies. That could be a few minutes or several gallons. Use a downstream faucet and keep the water running steadily — flushing removes packing material and disinfectants used during manufacturing.
Check for trapped air pockets
Air in the lines can cause sputtering and a noticeable odor. To release air, loosen a downstream faucet fitting or aerator briefly until flow becomes steady, then retighten. Open a few faucets at different heights (lowest and highest in the house) to help purge air from the system.
Inspect connections and sanitary fittings
Look for any caps, sanitary covers or fittings left open during installation. Tighten all compression nuts and push-fit connections and replace any damaged seals. If you find an open sanitary cap inside the housing area, remove the cartridge, rinse the housing, replace the cap correctly and reinstall the cartridge.
Run multiple gallons if the filter contains carbon
Carbon filters commonly need extra flushing to remove packing odors. Run several gallons (or the manufacturer-recommended volume) of water through the cartridge. If the smell is from carbon dust or factory odor, it usually fades after this extended flushing.
What Not to Do
- Avoid removing the filter while the system is pressurized — that risks a spray of contaminated water and possible injury.
- Do not run the system without flushing a new filter; skipping the flush can leave packing material or disinfectants in your plumbing.
- If smells persist after proper flushing, or if fittings leak after installation, call a professional rather than trying risky repairs yourself.
When to Call a Professional
- If a strong chemical or rotten-egg smell remains after thorough flushing and air purging.
- If you see persistent leaks at connections after tightening or replacement of seals.
- If you’re unsure whether the bypass valve or plumbing is configured correctly, or if water quality seems worse after install.
Safety Notes
- Shut off the water supply and relieve system pressure before touching fittings or changing cartridges.
- Wear gloves and eye protection when working with plumbing or contaminated filters.
- Dispose of used cartridges according to manufacturer guidance.
- Do not attempt internal repairs while the system is pressurized; isolate and depressurize the line first.
Common Homeowner Questions
- Why does a new carbon filter smell like plastic or dust? Short answer: manufacturing packing and carbon dust — it should clear after flushing.
- How long should I flush the filter? Follow the manufacturer’s instructions, often several minutes or a few gallons; carbon filters may need more.
- Is a brief odor dangerous? Usually not if it clears after flushing, but persistent or strong chemical/rotten smells warrant a professional check.
More in this topic
For more related fixes and similar symptoms, see Sewer Gas Smell from Floor Drains.