Why Extended Flushing Without Tank Filling Is Required During Initial RO System Startup| Insights by AQUALITEK

What Is Initial Startup Flushing?

Initial startup flushing refers to operating the RO system:

•With permeate diverted to drain, not the storage tank

•At low or controlled pressure

•For an extended period (often several hours)

This process applies to:

•Newly installed RO systems

•Systems after major modification

•Systems with newly installed membranes or pretreatment media

Key Reasons for Extended Flushing Without Filling the Tank

1. Removal of Preservatives from New RO Membranes

New RO membranes are shipped with chemical preservatives, such as:

•Sodium metabisulfite (SMBS)

•Glycerin-based protection agents

These chemicals:

•Are not suitable for consumption or industrial use

•Can cause odor, taste, or downstream contamination

Extended flushing ensures complete removal of preservatives before product water is collected.

2. Elimination of Installation Debris and Manufacturing Residues

New systems often contain:

•Dust and metal shavings from piping

•Glue, grease, and sealing compounds

•Carbon fines from pretreatment filters

Without sufficient flushing, these contaminants can:

•Enter the product water tank

•Pollute downstream processes

•Cause long-term water quality issues

3. Prevention of Early Membrane Fouling

During early operation:

•Flow paths are unstable

•Fine particles may still be present

•Pretreatment performance is not fully stabilized

Sending this water to the tank risks:

•Fouling membranes prematurely

•Contaminating storage tanks and pipelines

Flushing protects both membranes and the entire downstream system.

4. Stabilization of Operating Parameters

New systems require time for:

•Pressure to stabilize

•Flow rates to balance

•Conductivity readings to normalize

Initial permeate often shows:

•Elevated conductivity

•Unstable pH

•Fluctuating flow

Only after extended flushing do readings reflect true operating performance.

5. Avoidance of Biological Contamination

Preservatives, organic residues, and stagnant water can:

•Promote bacterial growth

•Create biofilm risks in tanks

By flushing to drain:

•Contaminated water is removed

•Clean baseline conditions are established

Once water enters the tank, contamination becomes much harder to eliminate.

6. Protection of Product Water Storage Tanks

Product tanks are designed for qualified water only.

If contaminated water enters:

•Tank cleaning may be required

•Disinfection becomes necessary

•Production may be delayed

Preventing contamination is far more efficient than corrective cleaning.

How Long Should Initial Flushing Last?

Typical industry practice:

•2–6 hours for small systems

•8–24 hours for large industrial RO systems

Flushing should continue until:

•Permeate conductivity stabilizes

•No odor is detected

•Water meets quality specifications

Always follow membrane supplier and system manufacturer guidelines.

Best Practices During Initial Flushing

✔ Divert permeate to drain
✔ Operate at low or staged pressure
✔ Monitor conductivity and pH trends
✔ Do not rush tank filling
✔ Record baseline operating data

Common Mistakes to Avoid

❌ Filling the product tank too early
❌ Judging water quality by appearance only
❌ Ignoring odor or conductivity fluctuations
❌ Skipping flushing to save time

These mistakes often lead to long-term operational problems.

Conclusion

Extended flushing without filling the tank during initial RO system startup is a critical protective measure. It removes preservatives, debris, and unstable water, stabilizes system performance, and prevents contamination of storage tanks and downstream processes. Skipping or shortening this step can compromise water quality and significantly increase maintenance costs later.