Reverse osmosis is the filtration behind most of the drinking water sold and dispensed in Thailand, from the 20-litre jugs delivered to offices to the refill kiosks outside convenience stores. It is effective, affordable and well understood. It also has a reputation for producing "empty" water, and that reputation is partly deserved. This article sets out what RO water is, where it is strong, where it falls short and why the systems we install put the minerals back.
RO water is water pushed through a membrane fine enough to hold back dissolved contaminants, including heavy metals and salts. The advantage is clean, consistent water from any mains supply. The drawback is that the membrane also removes calcium and magnesium, leaving flat, slightly acidic water. Remineralisation restores those minerals and raises the pH.
What RO water is
Reverse osmosis works by applying pressure to push water through a semi-permeable membrane. The membrane in Minairal Pure systems is rated at 0.0001 micron: water molecules pass, and most dissolved substances do not. What is held back is flushed away as reject water. On its own, the membrane is only the middle of the process. A complete system in Thailand usually runs five stages: pre-filtration for sand, rust and chlorine, the membrane itself, post-carbon polishing for taste and smell, and, on systems built for drinking rather than just purity, a mineral stage and UV sterilisation. The full sequence on our systems is described on the Pure range page.
The pros of RO water
- It removes what tap water in Thailand can carry. Dissolved metals, salts, pesticide residues and the by-products of chlorination are held back by the membrane, along with sediment and most microbes. Our guide on tap water in Thailand explains where those contaminants come from.
- The output is stable. Because the source is the water line, an RO system produces the same water on a dry day in March and a wet day in September. The Pure membrane is rated at 75 gallons a day, roughly 12 litres an hour.
- It is economical per litre. Once the system is installed, the running cost is the filter cartridges and very little electricity: a Pure machine draws around 40 to 50 W while cooling, a few baht a month. For a family or a small office, that compares well with bottled water over a year.
- It removes the taste of chlorine. The carbon stages before and after the membrane take out the smell many people associate with tap water.
- It is compact and quick to install. A countertop or floor-standing unit connects to the existing line, typically in under an hour.
The cons of RO water
- It strips the minerals. The membrane does not know the difference between lead and calcium. It removes both. Plain RO water has very low total dissolved solids and tastes flat.
- It is slightly acidic. With the buffering minerals gone, dissolved carbon dioxide pulls the pH of plain RO water below neutral. The water is not harmful, but it is not the pH most people expect from a drinking water.
- It produces reject water. Some of the incoming water carries the concentrated contaminants to the drain. The ratio depends on the membrane, the pressure and the incoming water, and it is worth asking about when comparing systems.
- It needs a water line and pressure. RO is not an option where there is no reliable mains supply. On islands and in villas on trucked water, that is exactly the case; there, an air-to-water system that produces drinking water from humidity is the alternative.
- It needs regular filter changes. On Pure systems the pre-filter is replaced every four months and the membrane, post-carbon and mineral filters every twelve.
Why remineralisation matters
The mineral question is the one that comes up most, and it deserves a straight answer. Drinking water is not the main source of calcium or magnesium in a normal diet; food is. But water with no minerals at all has been studied for a reason. The World Health Organization published a review, Nutrients in drinking-water (2005), that examined the consequences of long-term consumption of demineralised water, including water from desalination and membrane treatment, and what an optimal reconstitution of that water would look like. The practical conclusion of that work for a system builder is simple: if you take the minerals out, put them back.
There is also the matter of taste. Minerals are what make water taste like water. Plain RO water is often described as flat or thin; remineralised water has body, and that is what people notice first when they switch.
How Minairal Pure systems remineralise
After the membrane and the post-carbon stage, water passes through a mineral filter using Biocera technology from Korea. The filter releases calcium, magnesium, potassium and sodium into the water, bringing total dissolved solids to 40 to 80 ppm and the pH to an alkaline 8.5 and above. The stored water is then protected by continuous UV-C sterilisation and internal recirculation, and dispensed hot at 90°C or cold at 4°C. TDS and pH are checked during routine maintenance, and under the business service plan the water is tested once a year by an independent ISO 17025 accredited laboratory. The treatment is set out in detail on our water quality page.
Plain RO, remineralised RO and bottled water compared
| Plain RO water | Remineralised RO (Minairal Pure) | Bottled water | |
|---|---|---|---|
| Dissolved contaminants | Removed by the membrane | Removed by the membrane | Depends on the brand and source |
| Minerals | Very low | Calcium, magnesium, potassium, sodium restored, 40 to 80 ppm TDS | Varies widely |
| pH | Slightly acidic | 8.5 and above | Varies |
| Taste | Flat | Rounded | Varies |
| Supply | From the water line, stable | From the water line, stable | Deliveries, storage, plastic |
| Testing | Rarely | TDS and pH at each visit; annual ISO 17025 lab test on the business plan | By the bottler |
Is RO water right for your site?
If you have a reliable mains connection and want the simplest route to good drinking water, remineralised RO is the answer for most offices, restaurants, clinics and homes. A restaurant or café gets the same water for the kitchen, the bar and the staff, without the deliveries. For a house or apartment, the Pure Countertop and Pure Floor are listed on our online shop at ฿36,000 and ฿39,000. For a business site, request a site assessment and we come back with a configuration and a maintenance plan. If you are unsure whether RO or air-to-water fits your situation, our guide comparing air-to-water, reverse osmosis and bottled water goes through the three side by side.
Frequently asked questions
Is RO water safe to drink every day?
Yes. Reverse osmosis water is clean water. The question raised by the WHO review is about long-term consumption of water with no minerals at all, which is why remineralised RO is the better everyday option. This article is general information, not medical advice. Other wellness trends such as hydrogen-enriched water bottles are covered separately.
Does RO remove all minerals?
It removes most of them, together with the dissolved contaminants. That is why a mineral stage after the membrane matters: Minairal Pure systems restore calcium, magnesium, potassium and sodium to 40 to 80 ppm.
Is RO water acidic?
Plain RO water tends to be slightly acidic once the buffering minerals are gone. Remineralised RO water from a Pure system has a pH of 8.5 and above.
What is the difference between RO water and air-to-water?
RO treats water from the mains; air-to-water condenses it from humidity and then filters, sterilises and remineralises it. Both end with the same mineral profile on Minairal systems. RO needs a water line and gives stable output; air-to-water needs none and suits sites with no reliable supply.
How often are RO filters replaced?
On Pure systems the pre-filter is replaced every four months, and the membrane, post-carbon and mineral filters every twelve months, by Minairal technicians.
