Why is reverse osmosis water salty? Common Causes and Fixes

November 11, 2025 •

4 min read

Approximately 1% of the world's drinking water comes from reverse osmosis (RO) systems. A salty taste in this purified water can be alarming. Understanding why is reverse osmosis water salty often points to a fixable problem with a component rather than system failure.

Quick Summary

A salty taste in RO water usually results from a faulty membrane, a malfunctioning water softener, or improper flushing of new filters. Testing total dissolved solids (TDS) and performing specific maintenance can resolve the issue.

Key Points

Failing RO Membrane: The most frequent cause of salty RO water is a worn-out membrane that allows dissolved salts to pass through.
Water Softener Malfunction: A faulty water softener can introduce a salty brine solution into the RO supply, especially after an interrupted regeneration cycle.
Check TDS Levels: A TDS meter can verify if the membrane is failing by measuring the reduction of dissolved solids; a reduction below 90-95% is a red flag.
Initial Flushing Is Crucial: New RO systems or recently replaced filters must be properly flushed to eliminate manufacturing residues and carbon dust that can cause a bad taste.
Regular Maintenance Is Key: Proactive filter and membrane replacement, along with system sanitization, prevents buildup and ensures consistent, great-tasting water.

The Core Culprit: A Failing RO Membrane

Reverse osmosis works by pushing water through a semi-permeable membrane designed to block dissolved salts, minerals, and other contaminants. The membrane is central to the system, and its failure is the most common reason for a sudden salty taste. As the membrane ages and degrades, its pores can enlarge or tear, which lets salt ions through and contaminates the filtered water. This is especially common if the system hasn't been regularly maintained, or if the source water has high levels of Total Dissolved Solids (TDS). A significant increase in the TDS levels of the purified water is a strong indicator of membrane failure.

Water Softener Issues Affecting Your RO System

For homes with a water softener before the RO system, a faulty softener can be the source of the problem. Water softeners use a brine solution (saltwater) to regenerate the resin beads that remove hard minerals like calcium and magnesium. If the water softener's regeneration cycle fails or a valve malfunctions, it can introduce salty brine into your household's water lines, which then feeds into the RO system. An improperly functioning brine valve, a clogged injector, or incorrect control settings can all lead to this contamination.

How to Identify Softener-Related Issues

Regeneration Cycle Interruptions: A power outage during a regeneration cycle can halt the process, leaving residual brine in the resin tank.
Clogged Valves: A buildup of debris can clog the brine injector valve, causing it to draw in too much brine or not rinse properly.
Low Water Pressure: Insufficient water pressure can prevent the softener from completing a proper rinse cycle, allowing salty water to escape.

Improper Flushing of a New System

When a new RO system is first installed or after a filter replacement, it requires proper flushing. New components, especially the carbon filters, may contain residual carbon dust or manufacturing debris. Additionally, the system's storage tank has a rubber bladder that can impart a rubbery or plastic taste if not flushed sufficiently. Insufficient flushing means these residues remain in the system, causing an initial salty or unpleasant taste. Most manufacturers recommend flushing the first two to three full tanks of water before consumption to resolve this issue.

Other Less Common Reasons for Salty Taste

While membrane failure and water softener problems are the most likely causes, other factors can also contribute to a salty taste:

Stagnant Water in the Tank: If the RO system isn't used frequently, water sitting in the storage tank for an extended period can develop a stale, or even a musty, off-flavor. Regular flushing is necessary to prevent this.
High Source Water TDS: If the initial source water has extremely high TDS levels (over 800 mg/L), the RO system might struggle to remove all the salt, resulting in a noticeably salty taste, even when functioning correctly.
Air in the System: Entrapped air from newly installed filters can affect the taste of the first few tanks of water, causing an unpleasant flavor that eventually disappears.

Comparison: Membrane Failure vs. Water Softener Issues


Feature	Failed RO Membrane	Water Softener Malfunction
Symptom	Gradual increase in salty taste over time.	Sudden onset of salty taste, possibly after regeneration or power outage.
Associated Taste	Can be salty, metallic, or earthy, especially if minerals were reintroduced.	Primarily a salty brine taste.
Diagnostic Tool	High Total Dissolved Solids (TDS) reading in filtered water.	Water tastes salty from the main tap, not just the RO faucet.
System Indication	Slow water flow and high wastewater ratio may occur.	No change in RO flow, but salty water is present.
Common Solution	Replace the RO membrane.	Repair or adjust the water softener's settings or valves.

How to Fix Salty Reverse Osmosis Water

Test Your Water's TDS: Use a TDS meter to check both source water and RO-filtered water. A healthy RO system should show a 90-95% reduction in TDS. If the TDS level is high, the membrane is likely compromised.
Replace the RO Membrane: If TDS is high and the membrane is old (typically 2-3 years old), replacement is the most direct solution. Follow manufacturer guidelines during replacement.
Perform Proper Flushing: For new systems or filters, flush several full tanks of water. Don't consume the water until the taste has normalized.
Inspect Your Water Softener: If a softener is present, check the regeneration cycle and inspect valves for clogs or leaks. Run a manual regeneration cycle to see if that resolves the issue.
Address Stagnant Water: If the RO system has been unused for a while, flush the entire tank to ensure you are drinking fresh water.
Consider Remineralization: If the water tastes 'flat' after being purified and you desire a better taste, an alkaline or remineralization post-filter can reintroduce healthy minerals.

Conclusion

While a salty taste in reverse osmosis water is a clear sign that something is amiss, the cause is often straightforward to identify and fix. By troubleshooting the system, checking for a worn-out RO membrane, or investigating a potential water softener problem, the RO system can be restored to its proper function and enjoy clean, fresh-tasting drinking water once again. Regular maintenance is key to preventing these issues and ensuring the longevity of your home filtration system. For more technical details on the reverse osmosis process, you can consult resources like the NDSU Agriculture publication.

For additional information about the reverse osmosis process, please refer to this article from the NDSU Agriculture publication: https://www.ag.ndsu.edu/publications/environmental-systems/reverse-osmosis-water-treatment-for-homes

Frequently Asked Questions

A digital TDS meter can be purchased online or at most hardware stores. Collect samples of tap water and RO water, and test both. A healthy RO system should show a significant reduction, typically 90% or more, in the TDS level of the filtered water.

The lifespan of an RO membrane varies based on water usage and source water quality, but it generally needs to be replaced every 2 to 3 years. If a drop in water quality, reduced flow rate, or a salty taste is noticed, it may be time for replacement sooner.

Yes, a new system can taste salty or have an off-flavor initially. This is often due to manufacturing residues or carbon dust from the new filters. You must properly flush the system by running and emptying the first few tanks of water before drinking.

A properly functioning RO system should reduce the TDS level by 90-95% or more. The specific level depends on the source water's TDS, but it should be significantly lower than the tap water.

No, a correctly functioning water softener should not make RO water salty. However, if the softener malfunctions, particularly during its regeneration cycle, it can push salty brine into the RO system, leading to a temporary salty taste.

If the salty taste continues after a membrane replacement, the issue may lie with a malfunctioning water softener, improper flushing, or a rare issue with another system component like a flow restrictor. Check the softener and ensure proper flushing was performed.

While the immediate health risks are generally low, a persistent salty taste indicates a system malfunction that isn't filtering properly. The high TDS levels mean you are not getting the purified water you expect. It is best to troubleshoot and fix the system to ensure it's functioning correctly.