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PT1: Industrial Reverse Osmosis Troubleshooting: 15 Reasons Your RO System Is Producing Less Water (And Exactly How to Fix Each One)
Jul
Why Is My Reverse Osmosis System Producing Less Water?
When an industrial reverse osmosis (RO) system begins producing less water than expected, many operators immediately assume the membranes have reached the end of their life. In reality, that is often one of the least common reasons.
Most reductions in RO production are caused by changes elsewhere in the system. A blocked pre-filter, reduced feed pressure, incorrect recovery settings or poor feed water quality can all dramatically reduce permeate flow long before the membranes themselves require replacement.
The good news is that most of these issues can be identified quickly if you know what to look for.
At Industrial Water Equipment Ltd (IWE) we design, manufacture and support industrial reverse osmosis systems across the UK. We’ve diagnosed everything from simple cartridge filter blockages to heavily scaled membrane arrays and failing high-pressure pumps. In many cases, the solution is far simpler—and far less expensive—than replacing the entire membrane set.
This guide explains the 15 most common causes of low production in industrial reverse osmosis systems, how to diagnose each issue and, most importantly, how to fix it before it impacts production.
Whether your RO system produces 150 litres per hour or 50,000 litres per hour, the same troubleshooting principles apply.
Understanding How an RO System Produces Water
Before looking at faults, it’s worth understanding what determines the amount of purified water an RO system can produce.
Reverse osmosis works by applying pressure to feed water, forcing it through a semi-permeable membrane. The membrane allows water molecules to pass while rejecting dissolved minerals, salts and many other contaminants.
Every RO system produces two separate streams:
- Permeate – the purified product water.
- Reject (Concentrate) – the contaminants removed from the feed water.
The volume of permeate produced depends on several factors working together:
- Feed water pressure
- Feed water temperature
- Membrane condition
- Feed water quality
- Recovery rate
- Pump performance
- Effective pre-treatment
If just one of these variables changes, overall production can fall significantly.
That is why successful troubleshooting involves looking at the complete system rather than focusing on the membranes alone.
Before You Replace Anything…
One of the biggest mistakes we see is expensive components being replaced before the basic checks have been carried out.
Before ordering new membranes or pumps, record the following operating data:
- Feed pressure
- Pump discharge pressure
- Differential pressure across pre-filters
- Permeate flow rate
- Reject flow rate
- Feed conductivity
- Product conductivity
- Feed water temperature
Comparing today’s readings against the system’s original commissioning figures often identifies the problem in minutes.
Keeping a simple logbook of these readings is one of the most effective preventative maintenance tools available.
Quick Troubleshooting Guide
| Symptom | Most Likely Cause | First Check |
|---|---|---|
| Low water production | Blocked pre-filters | Differential pressure |
| High operating pressure | Membrane scaling | Membrane pressure |
| Poor water quality | Damaged membrane | Conductivity |
| Sudden production loss | Pump or valve fault | Feed pressure |
| Gradual reduction | Fouling | Pressure trend |
| Seasonal reduction | Cold feed water | Water temperature |
| High reject flow | Recovery settings | Flow meters |
1. Blocked Sediment Pre-Filters
Why it happens
Every industrial RO system relies on pre-filtration to remove suspended solids before water reaches the membranes. Sediment cartridges trap rust, sand, silt, pipe scale and other particulate matter that would otherwise foul the membrane surface.
Over time these cartridges become increasingly blocked. As resistance increases, less water reaches the high-pressure pump, reducing the volume available for treatment.
Common symptoms
- Gradual reduction in permeate flow
- Increased pressure drop across the filter housing
- High-pressure pump sounds strained
- Pump cavitation in severe cases
- Increased energy consumption
How to diagnose it
The simplest method is to compare the inlet and outlet pressure gauges across the sediment filter housing.
A noticeable pressure drop indicates the cartridges are restricting flow.
If no gauges are fitted, installing them is a worthwhile upgrade that can save significant maintenance costs.
How to fix it
Replace the cartridges with the correct micron rating specified for your system.
Avoid installing finer cartridges than required. While they may appear to offer better filtration, unnecessarily fine cartridges can increase pressure loss and reduce production.
Prevention
Rather than replacing filters every month regardless of condition, monitor the differential pressure and change them when performance begins to decline. This approach often reduces consumable costs while ensuring consistent RO performance.
IWE Tip: A blocked £10 filter cartridge can reduce the performance of a £1,000 membrane set. Always check the simplest components first.
2. Exhausted Carbon Filters
Why it happens
If your RO system treats chlorinated mains water, activated carbon filtration is essential.
Thin-film composite RO membranes are extremely sensitive to chlorine. Even relatively low concentrations can permanently damage the membrane surface, reducing both water quality and production.
Carbon filters remove chlorine before it reaches the membranes, but they have a finite capacity.
Once exhausted, chlorine begins to pass through the media and slowly attacks the membrane.
Common symptoms
- Gradual decline in rejection performance
- Product conductivity increases
- Lower permeate flow
- Membranes requiring replacement much earlier than expected
How to diagnose it
Carry out a free chlorine test immediately after the carbon vessel.
Any detectable chlorine indicates the media has reached the end of its useful life or requires regeneration.
How to fix it
Replace or regenerate the activated carbon media.
Never continue operating an RO system if chlorine is present downstream of the carbon filter.
Prevention
Regular chlorine testing is considerably more reliable than simply changing carbon on a calendar schedule.
It is often possible to maximise media life while still protecting the membranes by monitoring chlorine breakthrough rather than relying on estimated service intervals.
3. Membrane Fouling
Why it happens
Membrane fouling occurs when contaminants build up on the membrane surface, making it increasingly difficult for water to pass through.
Unlike scaling, fouling isn’t caused by dissolved minerals—it results from deposits such as:
- Organic matter
- Fine suspended solids
- Iron
- Manganese
- Colloidal particles
- Oils and greases
As these deposits accumulate, permeate flow gradually falls while operating pressure rises.
Common symptoms
- Gradual loss of production
- Higher differential pressure
- Stable rejection performance
- Increasing energy consumption
How to diagnose it
Compare current operating pressures with historical records.
If feed pressure remains unchanged but membrane pressure steadily increases while permeate production falls, fouling is likely.
A membrane autopsy or cleaning trial can confirm the type of fouling present.
How to fix it
Carry out a suitable Clean-in-Place (CIP) using chemicals appropriate for the fouling type.
Organic fouling and inorganic fouling require different cleaning solutions, so identifying the contamination is essential.
Cleaning should begin as soon as reduced performance is identified. Leaving fouled membranes in service for extended periods often allows deposits to harden, making them significantly more difficult to remove.
Prevention
Effective pre-treatment is the best defence against membrane fouling.
Maintaining low SDI (Silt Density Index), changing cartridge filters when required and ensuring feed water remains within design parameters all help maximise membrane life.
