RO membrane cleaning is most effective when triggered early, based on changes in normalized performance—not when performance has already significantly declined.

The challenge is knowing when those changes justify cleaning.

When should RO membranes be cleaned?

RO membranes should be cleaned when any of the following normalized performance changes occur:

• Normalized permeate flow drops by 10%
• Normalized salt passage increases by 5–10%
• Normalized pressure drop increases by 10–15%

If one or more of these thresholds are reached, cleaning should be initiated to restore performance and prevent further fouling or scaling.

Use this quick checklist to determine whether cleaning is needed now:

Permeate flow

• Has normalized permeate flow decreased by 10% or more?
  → Yes: Cleaning is recommended
  → No: Continue monitoring

Salt passage (rejection)

• Has normalized salt passage increased by 5–10%?
  → Yes: Cleaning is recommended
  → No: Continue monitoring

Pressure drop

• Has normalized pressure drop increased by 10–15%?
  → Yes: Cleaning is recommended
  → No: Continue monitoring

✅ If you answered “yes” to any of the above:
Cleaning should be performed.

What happens if cleaning is delayed?

Timing is critical for effective membrane cleaning.

• Fouling and scale deposits become more difficult to remove over time
• Cleaning effectiveness decreases as deposits harden or embed into the membrane surface
• In some cases, delayed cleaning may not fully restore performance

Acting early improves the likelihood that cleaning will successfully recover system performance. 

After cleaning: what to expect

Once cleaning is complete:

• Permeate should be diverted to drain until it meets quality requirements
• Normal operating conditions should be re-established gradually
• System performance should be re-evaluated using normalized data

These steps help ensure:

• stable system restart
• accurate assessment of cleaning effectiveness

When cleaning may not be enough

Cleaning is often the first corrective step, but not all issues are recoverable.

Further investigation is needed if:

• performance does not improve after cleaning
• multiple symptoms are present (e.g., flow loss + salt passage increase)
• performance continues to decline

➡️ For decision guidance, see Clean or Replace? A Practical Guide for FilmTec™ Elements 

Need more detail?

For full cleaning procedures, chemical selection, and safety guidance: ➡️ Download the FilmTec™ Cleaning Procedures Manual (PDF)

(Use this alongside the checklist above to execute cleaning correctly.)

Quick reference