Desalination Rate vs. TDS Value: Which One Should You Look at to Assess a Water Purifier’s Filtration Effectiveness?

When buying a water purifier or testing their home’s water quality, many people come across two terms: desalination rate and TDS value. Some use a TDS meter to take a reading—getting anxious if the number is high and relieved if it’s low. Others tell you not to focus solely on TDS, but to look at the desalination rate instead. So which one is more important? Let’s clarify this today.

I. Understanding the Two Concepts
1. What Is Desalination Rate?
Simply put, desalination rate is the percentage of dissolved salts and ionic contaminants that a water purifier can remove from water. It is a professional metric for measuring the core filtration performance of RO (reverse osmosis) membranes and applies exclusively to RO systems. A higher desalination rate indicates greater filtration precision of the RO membrane and higher purity of the treated water. For standard, certified household RO water purifiers, the desalination rate typically remains stable at 90% or higher.

2. What is the TDS value?
TDS (Total Dissolved Solids) refers to the total amount of dissolved impurities in water, measured in ppm. This includes calcium and magnesium ions, minerals, salts, and certain soluble contaminants. This is the value we measure daily using a TDS meter.

II. The Core Role of Desalination Rate
1. It directly reflects the filtration precision and quality of the RO membrane and is a professional, core performance parameter.
2. It indicates the system’s ability to remove harmful substances in ionic form, such as heavy metals, nitrates, fluorides, and salts.
3. The higher the desalination rate, the better the filtration effect and the higher the purity of the treated water. In short: Desalination rate is the key indicator for determining whether an RO membrane is “good” or not.

III. The Core Functions of TDS Values
1. It provides a quick and intuitive indication of the amount of dissolved substances in water; generally, the higher the value, the higher the impurity content.
2. It serves as a simple, at-home testing method, allowing users to easily measure and compare changes in TDS values before and after water purification.
3. It helps determine whether the RO reverse osmosis water purifier is functioning normally and whether the filter cartridge needs replacement.
In summary: The TDS value acts as a “barometer” for monitoring the daily status of your water purifier.

IV. Limitations of Both Metrics—Do Not Overlook Them
Limitations of Desalination Rate
1. Applicable only to RO (reverse osmosis) water purifiers; this metric is not available for models using ultrafiltration (UF) or nanofiltration (NF).
2. It is a professional data point from laboratory or factory testing and cannot be monitored in real-time using standard household tools.
3. It does not indicate the removal effectiveness of residual chlorine, organic compounds, bacteria, or viruses; performance must be evaluated in conjunction with other filter cartridge capabilities.

Limitations of TDS Values
1. It measures total dissolved solids only and cannot distinguish between beneficial minerals and harmful heavy metals or chemical contaminants.
2. For non-RO water purifiers (such as UF or MF systems), TDS values remain virtually unchanged and cannot be used to evaluate filtration effectiveness.
3. A low value does not guarantee absolute sterility or the absence of organic matter, nor does a high value mean the water is undrinkable

Conclusion for ordinary households:
When selecting a water purifier: Check the desalination rate (RO models must be ≥90% to be considered合格)
During daily use: Monitor changes in TDS values (compare before and after filtration, rather than focusing solely on absolute values)
Don’t be misled by a single number: TDS dropping from 200 to below 10 → RO system functioning normally; TDS originally only 50 → below 5 after filtration; TDS unchanged in an ultrafiltration system → normal, as it does not remove dissolved salts and cannot be evaluated by TDS
Desalination rate and TDS values are not mutually exclusive; rather, they represent a division of labor between professional evaluation and daily monitoring. Desalination rate determines the “fundamental quality” of the RO system, while TDS values help you determine whether it is functioning “properly” at the moment.

When buying a water purifier, prioritize RO models with high desalination rates; when using one, regularly monitor changes in TDS values before and after filtration. Once you understand both, you won’t be misled when choosing a water purifier. What type of water purifier do you use at home? Do you usually measure TDS? Feel free to leave a comment and share your thoughts!