How do you choose between RO (reverse osmosis) and ultrafiltration? Don’t just buy anything; base your decision on your own water quality.

How do you choose between RO (reverse osmosis) and ultrafiltration? Don’t just buy anything; base your decision on your own water quality.
RO or ultrafiltration? This question has puzzled so many people. On one hand, there are RO systems promising ‘deep purification and worry-free drinking water’; on the other, ultrafiltration systems claiming to ‘retain minerals and produce zero wastewater’. Everyone seems to have a valid point, leaving you increasingly confused. In reality, there’s no need to agonise over which water purifier to choose – the key lies in a single word: water. The quality of your household water determines which path you should take.

What is the core difference between RO and UF?
The fundamental difference between the two lies in filtration precision. The pore size of an RO membrane is approximately 0.0001 micrometres, equivalent to one millionth of the diameter of a human hair; the pore size of a UF membrane ranges from 0.01 to 0.1 micrometres. This difference in precision is roughly 100-fold, which determines what each system can block and what it allows through.
RO membranes can intercept almost everything—heavy metal ions, viruses, bacteria, calcium and magnesium ions, and antibiotic residues. The TDS value of the treated water can usually be reduced to below 10, making it virtually pure water. Ultrafiltration membranes can trap sediment, rust, bacteria, colloids and large organic molecules, but are largely ineffective against heavy metals, viruses and dissolved salts; the TDS value of the treated water is similar to that of the source water.
Another obvious difference: RO systems require electricity to power a booster pump and produce wastewater (mainstream models have a pure water to wastewater ratio of 1:1 to 3:1); Ultrafiltration systems require no electricity and produce no waste water, operating solely on tap water pressure. This is why many people choose ultrafiltration – it saves electricity and water, and is simple to maintain.
How to choose based on local water quality Before selecting a water purifier, spend a few quid on a TDS pen to test your own tap water. Take a water sample 30 seconds after turning on the tap in the morning, measure three times and take the average; this figure is more reliable than any sales recommendation.
A TDS meter is the most intuitive tool for assessing water quality
In areas where the TDS value is below 100, the water quality is generally good, with municipal supplies meeting standards and relatively new pipework. In such areas, ultrafiltration is sufficient; it filters out sediment and bacteria to improve taste, retains minerals and does not waste water. This assumes that household members are accustomed to boiling water before drinking and do not drink directly from the tap.
Where the TDS value exceeds 200 and kettles develop thick limescale deposits on the inside, the area is essentially a hard water zone. In most northern cities and the north-western regions, TDS levels frequently reach 300–500. Ultrafiltration is simply ineffective against this type of water—calcium and magnesium ions pass straight through the ultrafiltration membrane, and limescale will still form. Reverse osmosis (RO) is essential, with a desalination rate of over 95%, ensuring the kettle’s base remains spotless after boiling.
TDS values between 100 and 200 fall into a grey area, and the choice depends on your needs. If you have infants requiring formula, elderly family members who prefer room-temperature boiled water, or if you have specific requirements for drinking water, opt for RO. If everyone in the family boils their water and you simply wish to improve the taste and remove any off-odours, ultrafiltration is sufficient.
There is also a special category: older housing estates or secondary water supply systems. Ageing pipework can easily leach heavy metals; even if the TDS reading appears low, you must not be complacent. IDC’s 2025 water purifier user survey data shows that the complaint rate for gastrointestinal discomfort caused by the misuse of ultrafiltration units for direct drinking in southern regions reached as high as 17.3%, far exceeding the 0.9% rate for RO models. In such circumstances, RO is virtually the only safe choice.

💡 Purchasing Tips
TDS < 100 and no risk of heavy metals → UF may be considered; TDS > 200 or limescale build-up when boiling water → RO is essential; between 100–200, it depends on your needs. Do not rely solely on geographical assumptions; water quality can vary significantly between different areas within the same city, so rely on actual test results.

Weigh up the pros and cons of RO before making a decision
The greatest advantage of RO is its thorough filtration. It removes over 99% of heavy metals, blocks all viruses and bacteria, reduces the TDS of the output water to single digits, and prevents limescale build-up in kettles for up to six months. For households with infants requiring formula milk or those sensitive to the taste of tea, RO is an absolute necessity.