How to Temporarily Assess Water Quality When an Online Conductivity Meter Fails| Insights by AQUALITEK

Introduction

Online conductivity meters are critical instruments in RO systems, providing real-time feedback on salt rejection and membrane integrity. However, in real-world operation, unexpected failures may occur due to:

•Sensor fouling

•Signal cable damage

•Transmitter malfunction

•Power or grounding issues

When the online conductivity meter suddenly stops working, operators cannot simply continue running the system blindly. This article outlines best temporary methods to assess water quality until the instrument is repaired or replaced.

Why Conductivity Monitoring Is So Important

Conductivity directly reflects:

•Total dissolved solids (TDS)

•Membrane salt rejection performance

•Potential membrane leakage or damage

Without reliable conductivity data, risks include:
❌ Supplying off-spec product water
❌ Failing to detect membrane rupture
❌ Undetected contamination entering downstream processes

Method 1: Use a Portable (Handheld) Conductivity Meter

Why This Is the Best Temporary Solution

A calibrated handheld conductivity meter can provide quick and accurate spot checks.

Best Practices

•Collect permeate samples from a clean sampling point

•Rinse the probe with permeate before measurement

•Measure multiple times to confirm consistency

Compare results with historical online readings under similar conditions.

Method 2: Compare Feed Water and Permeate Conductivity (Manual Sampling)

Even without online data, you can evaluate system performance by:

•Measuring feed water conductivity

•Measuring permeate conductivity

Calculate Salt Rejection

Salt Rejection (%)=(1−Permeate Conductivity/Feed Conductivity)×100

A sudden drop in rejection indicates potential membrane or seal issues.

Method 3: Monitor Conductivity Trends in Downstream Equipment

If the RO system feeds:

•EDI units

•Mixed-bed polishers

•Boiler feedwater systems

Then observe:

•EDI inlet conductivity

•Polisher exhaustion rate

•Boiler blowdown frequency

Abnormal changes often reflect hidden permeate quality deterioration.

Method 4: Observe System Operating Parameters

While not a direct substitute, changes in the following can signal water quality issues:

•Sudden increase in permeate flow

•Unexpected pressure drop reduction

•Abnormal recovery behavior

Good-looking and overly stable parameters can also indicate faulty sensors.

Method 5: Perform Simple On-Site Chemical Tests (If Applicable)

Depending on system requirements:

•Silica test kits

•Hardness test strips

•Chloride spot tests

These tests help detect specific contaminants that conductivity alone may not reveal immediately.

Method 6: Temporarily Divert Product Water from the Storage Tank

As a risk-control measure:

•Divert permeate to drain or recycle line

•Avoid sending water to critical processes

This is especially important for:

•Pharmaceutical

•Semiconductor

•Boiler feedwater applications

Common Mistakes to Avoid

❌ Trusting system operation without any verification
❌ Relying only on pressure and flow readings
❌ Continuing production for long periods without manual testing
❌ Ignoring historical performance benchmarks

Best Practice Recommendations

✔ Keep a calibrated handheld conductivity meter on site
✔ Record manual conductivity readings during instrument failure
✔ Repair or replace faulty sensors as soon as possible
✔ Include conductivity meter failure response in SOPs

Conclusion

When an online conductivity meter fails, water quality control must not stop. By using portable meters, manual comparisons, downstream indicators, and conservative operational decisions, operators can temporarily and safely assess permeate quality until normal monitoring is restored.

Proactive preparation and proper response procedures are key to maintaining RO system reliability and protecting downstream processes.