Best Guide: What Are the Possible Causes of an Off-Odor in RO Produced Water?| Insights by AQUALITEK

1. Why Should RO Water Normally Have No Odor?

A properly functioning RO system removes:

•Dissolved salts

•Organic matter

•Odor-causing compounds

•Microorganisms

Therefore, any noticeable odor is an abnormal condition and should be investigated immediately.

2. Common Causes of Off-Odor in RO Permeate

Cause 1: Contamination in the Storage Tank or Piping

This is the most common cause in household and industrial systems.

Possible sources:

•Biofilm buildup in storage tanks

•Mold growth due to long stagnation

•Food-grade bladder tanks aging

•Rubber materials releasing odor

•Poor hygiene of distribution piping

Typical smells: musty, earthy, rubber-like

Solutions:

•Clean and disinfect the tank

•Replace aged bladder components

•Flush piping with disinfectant (NaClO, H₂O₂)

•Avoid long-term stagnant water

Cause 2: Activated Carbon Post-Filter Exhaustion

If a post carbon filter (T33) is saturated, it may:

•Fail to remove residual odors

•Release microbial metabolites

•Produce slight chemical smell

Typical smells: chlorine-like, chemical, plastic

Solutions:

•Replace post carbon filter

•Ensure regular maintenance cycle

•Flush adequately after filter replacement

Cause 3: Biofouling or Contamination on the RO Membrane

If microorganisms colonize the membrane surface, permeate quality may drop.

Typical smells: musty, swampy, rotten water odor

Causes:

•Inadequate disinfection

•Long shutdown without proper preservation

•Pretreatment failure

•High TOC in feedwater

Solutions:

•Perform chemical cleaning (biocide/acid)

•Strengthen pre-filtration

•Ensure proper membrane preservation during shutdown

Cause 4: Chlorine Breakthrough Damaging the RO Membrane

When chlorine leaks through exhausted activated carbon:

•Membrane surface is oxidized

•The membrane loses rejection

•Organics pass through easily

•Permeate becomes odorous

Typical smell: chlorine-like, chemical

Solutions:

•Replace carbon filter

•Check residual chlorine

•Verify membrane integrity

Cause 5: Bacterial Contamination in Post-RO Accessories

Components such as:

•UV chambers

•Mineralization cartridges

•Alkaline cartridges

•Hollow fiber polishing filters

can become microbial hotspots if:

•They are used past service life

•They are not flushed properly

•Water stays stagnant for days

Typical smells: earthy, sour, musty

Solutions:

•Replace suspect cartridges

•Sanitize the system

•Improve flushing routine

Cause 6: Material Odor from New Components

New:

•tubing

•housings

•tanks

•O-rings
may release initial odors.

Typical smells: plastic, rubber

Solutions:

•Thoroughly flush system

•Sanitize with weak disinfectant

•Ensure NSF-certified food-grade materials

Cause 7: Source Water Odor Passing Through Due to Pretreatment Failure

If pretreatment is inadequate:

•High TOC

•Hydrogen sulfide (H₂S)

•Volatile organic compounds
may penetrate or overwhelm the RO system.

Typical smells: rotten egg (H₂S), fishy, earthy

Solutions:

•Check feedwater quality changes

•Replace pretreatment media

•Add activated carbon or aeration steps

3. How to Diagnose the Source of the Odor?

Step-by-step approach:

1.Smell the permeate directly from the RO membrane

If odor exists → membrane/post-filters issue

If no odor → tank/piping issue

2.Check storage tank and distribution piping

Most common biofilm location

3.Check post activated carbon filter (T33)

Replace if exceeded lifespan

4.Check feedwater odor

Source water may be the problem

5.Observe permeate conductivity trend

Sharp increase may indicate membrane damage

6.Test bacterial levels if necessary

4. How to Prevent Permeate Odor Long-Term

•Maintain regular flushing

•Replace filters on schedule

•Keep system disinfected during shutdown

•Use high-quality food-grade components

•Prevent long-term stagnation of water

•Install UV after storage tanks (industrial systems)

Conclusion

An off-odor in RO permeate is usually linked to:

•Biofilm growth

•Exhausted carbon filters

•Post-filter contamination

•Membrane fouling or oxidation

•Poor pretreatment

•New component odor

With systematic diagnosis and proper maintenance, the issue can be quickly identified and resolved.