What Are the Most Common Problems with RO Pure Water Systems and How to Fix Them?

When an RO pure water system malfunctions, production halts. The most common culprits are clogged prefilters (responsible for up to 70 percent of flow issues), membrane fouling that reduces rejection rates, and leaks from loose fittings. The immediate fix for low flow is inspecting and replacing the sediment and carbon prefilters if they have been in service for over 6 months. For a sudden drop in water quality (high TDS), the RO membrane itself likely requires replacement, typically every 2 to 3 years. Addressing these two points resolves the majority of operational complaints without the need for extensive system overhauls.

Diagnosing and Resolving Flow and Pressure Issues

Insufficient Product Water Flow

This is the most frequent complaint in industrial and commercial setups. The cause is usually a blockage in the pre-filtration stage or a fouled membrane. Sediment and carbon filters should be replaced every 6 to 12 months to prevent them from becoming a flow restriction point. If replacing the prefilters does not restore flow, the RO membrane may be scaled or fouled. Additionally, check the flow restrictor; if it is overly clogged or incorrectly sized, it can drastically reduce output.

For systems with a storage tank, low flow can also result from improper tank pressure. An empty tank should have an air pre-charge of 5 to 7 psi; if this drops, the bladder cannot push water out effectively.

Low Incoming Feed Pressure

RO systems are designed to operate within a specific feed pressure range, typically 40 to 60 psi. If the feed pressure drops below this, the booster pump may struggle, leading to low production or system shutdown via the low-pressure switch. Check the feed valve to ensure it is fully open and inspect for any kinks or blockages in the supply line.

Tackling Water Quality and Taste Complaints

High Total Dissolved Solids (TDS) or Bad Taste

A sudden increase in product water TDS indicates a failure in the membrane's rejection capability. While a slight increase is normal as a membrane ages, a sharp rise means the membrane is compromised. Common causes include chlorine damage (which oxidizes the membrane surface) or physical abrasion. If the incoming water contains more than 2.0 ppm of chlorine, the carbon prefilter must be replaced immediately to protect the new membrane.

Bad tastes and odors are often linked to the post-filter or biological growth. If the water tastes stale, sanitize the system and replace the post-filter.

Membrane Fouling and Scaling

Fouling is the accumulation of suspended particles, colloids, or microorganisms on the membrane surface. Scaling is the precipitation of sparingly soluble salts (like calcium carbonate) on the surface. Both lead to higher pressure drop and lower permeate flux. A well-maintained system operating on proper feed water should maintain stable rejection rates.

System Shutdown and Electrical Tripping

When an RO unit fails to start or trips immediately, the issue is either electrical or hydraulic. If the house breaker or GFCI trips, the system is drawing excessive current. This usually points to an overloaded circuit or a failing pump motor. The pump draws the highest current at startup, so sharing a circuit with other heavy appliances can cause this.

If the system starts but shuts down quickly (hydraulic trip), it is likely a pressure problem. The automatic shut-off (ASO) valve will trigger if the pump cannot generate enough pressure, often due to a clogged prefilter or a malfunctioning check valve. Inlet pressure below 40 psi is a primary cause of this cycling behavior.

Common RO System Faults and Diagnostic Indicators

Preventive Maintenance Schedule

Critical Replacement Intervals

Adherence to a strict maintenance schedule is the most effective way to prevent common RO problems. Neglecting replacements is the leading cause of system failure.

• Sediment Prefilter: Replace every 6 to 12 months to prevent fouling of the membrane.
• Carbon Prefilter: Replace every 6 to 12 months to ensure chlorine is removed and the membrane is protected.
• RO Membrane: Replace every 2 to 3 years, depending on feed water quality and usage.
• Post-filter: Replace annually during system sanitization to prevent taste issues.

System Sanitization

Biofilm growth is a frequent cause of fouling and taste issues. It is recommended to sanitize the entire system at least once a year or whenever the filters are changed. This involves flushing the system with a sanitizing agent (like a commercial RO sanitizer or diluted bleach) to eliminate bacteria that can survive in the plumbing.

Seasonal and Environmental Considerations

Environmental factors significantly impact RO performance. In winter, cold feed water causes the water viscosity to increase, leading to a drop in production by approximately 3 percent per 1 degree Celsius decrease in temperature. To compensate, either increase the feed pressure or use a feed water heater to maintain a temperature of 20 to 25 degrees Celsius during cold months.

For systems installed outdoors or in unheated spaces, freeze protection is critical. Water expands when frozen, which can crack membrane housings and rupture tubing. The system must be protected when temperatures drop below 5 degrees Celsius, and operation is prohibited below 0 degrees Celsius to prevent catastrophic damage.