In Part 1, we covered three of the most common reasons an industrial reverse osmosis (RO) system experiences reduced water production: blocked sediment filters, exhausted carbon filters and membrane fouling.

In this second part, we move on to three more issues that regularly affect industrial RO performance. These are often more difficult to identify because the symptoms can appear similar, yet each requires a different solution.

Understanding the difference between membrane scaling, inadequate feed pressure and high-pressure pump issues can save considerable time, reduce unnecessary membrane replacements and minimise costly production downtime.

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4. Membrane Scaling

Membrane scaling is one of the most common causes of declining RO performance, particularly in areas with hard water or where feed water chemistry changes over time.

Unlike membrane fouling, which is caused by contaminants collecting on the membrane surface, scaling occurs when dissolved minerals precipitate out of solution and form hard crystalline deposits.

Common scale-forming minerals include:

• Calcium carbonate
• Calcium sulphate
• Barium sulphate
• Silica
• Strontium sulphate

As scale builds up, it blocks the membrane surface, making it increasingly difficult for water to permeate through. This leads to higher operating pressures, lower permeate flow and increased energy consumption.

If left untreated, severe scaling can permanently damage membranes.

Common Symptoms

• Gradual reduction in permeate flow
• Increasing operating pressure
• Stable or slightly improved rejection
• Rising energy costs
• Reduced system recovery

How to Diagnose It

Review your operating data.

If permeate production has steadily declined while membrane pressure continues to increase, scaling should be considered.

Other indicators include:

• High feed water hardness
• Insufficient antiscalant dosing
• Incorrect recovery settings
• Poor softener performance

A membrane autopsy or CIP inspection will normally confirm the presence of scale deposits.

How to Fix It

Where scaling is identified early, a suitable chemical clean may restore much of the membrane’s original performance.

However, if scale has hardened over several months, cleaning becomes less effective and membrane replacement may be unavoidable.

It is also essential to correct the root cause before installing new membranes.

Replacing membranes without resolving scaling issues simply starts the cycle again.

Prevention

Scaling is largely preventable with appropriate pretreatment.

Good practice includes:

• Correct antiscalant dosing
• Maintaining water softeners
• Monitoring feed water hardness
• Regular conductivity testing
• Operating within the designed recovery rate

IWE Expert Tip: Many membrane failures blamed on “old age” are actually caused by scaling. Correcting feed water chemistry often doubles membrane life.

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5. Low Feed Pressure

Reverse osmosis relies entirely on pressure.

Without sufficient feed pressure, water cannot pass efficiently through the membrane, regardless of its condition.

Many production issues are ultimately traced back to an inadequate water supply rather than the RO itself.

Even a relatively small reduction in feed pressure can have a significant impact on permeate production.

Common Causes

• Restricted incoming mains supply
• Blocked pipework
• Undersized feed pumps
• Partially closed isolation valves
• Blocked strainers
• Excessive demand elsewhere within the factory

Common Symptoms

• Sudden reduction in water production
• Lower pump suction pressure
• Stable conductivity
• Pump cavitation
• Intermittent production issues

How to Diagnose It

Begin by checking the pressure entering the RO system.

Compare today’s reading with the commissioning figures or previous service records.

If the incoming pressure has reduced significantly, investigate upstream rather than immediately assuming an RO fault.

Inspect:

• Isolation valves
• Strainers
• Feed pumps
• Incoming water supply
• Pressure regulators

How to Fix It

The appropriate solution depends on the cause.

Possible remedies include:

• Cleaning blocked strainers
• Opening partially closed valves
• Replacing undersized pipework
• Installing or servicing a booster pump
• Repairing supply restrictions

Once the correct feed pressure is restored, production usually returns immediately.

Prevention

Feed pressure should be logged as part of routine maintenance.

Many modern RO controllers can record pressure trends automatically, allowing problems to be identified long before production is affected.

IWE Expert Tip: Don’t just record membrane pressure—always record feed pressure too. Without both figures, diagnosing performance issues becomes much more difficult.

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6. High-Pressure Pump Problems

The high-pressure pump is the heart of any reverse osmosis system.

Its role is to generate the pressure required for reverse osmosis to occur.

As pumps wear over time, their efficiency declines.

Mechanical wear, damaged impellers, worn seals or bearing failures all reduce pump performance.

Even if the membranes remain in excellent condition, insufficient pressure will dramatically reduce permeate production.

Common Symptoms

• Reduced water production
• Lower operating pressure
• Pump vibration
• Unusual noise
• Increased electrical consumption
• Intermittent pressure fluctuations

How to Diagnose It

Compare the pump’s discharge pressure against its design specification.

Check for:

• Excessive vibration
• Bearing noise
• Seal leakage
• Motor overheating
• Variable speed drive faults (where fitted)

If pressure cannot be achieved despite adequate feed water, the pump should be inspected by a qualified engineer.

How to Fix It

Depending on the fault, repairs may involve:

• Replacing mechanical seals
• Renewing bearings
• Repairing impellers
• Servicing the motor
• Replacing the complete pump

Modern energy-efficient pumps may also reduce operating costs compared with older equipment.

Prevention

Routine servicing remains the most effective way of extending pump life.

Regular inspection of:

• Bearings
• Couplings
• Seals
• Lubrication
• Motor alignment

can prevent many failures before they interrupt production.

Where pumps operate continuously, predictive maintenance programmes can significantly reduce unexpected downtime.

IWE Expert Tip: A noisy pump is rarely “just noisy”. Changes in sound or vibration often provide the earliest warning of developing mechanical problems.

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Key Takeaways from Part 2

By now we’ve covered six of the most common causes of reduced RO production.

The most important lesson is that membranes are not always to blame.

Many performance issues originate elsewhere within the system, and replacing membranes without diagnosing the root cause often leads to unnecessary expense.

Always investigate the entire process—from incoming feed water through to the high-pressure pump and membrane array—before replacing major components.

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Coming Up in Part 3

In the next instalment, we’ll look at three more common causes of low RO production:

• Cold Feed Water
• Incorrect Recovery Settings
• Faulty Concentrate Valves

These issues are frequently overlooked but can have a surprisingly large impact on system performance, particularly during seasonal changes or following commissioning adjustments.

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