RO Water: What It Is, What It Removes, and RO vs Mineral Water
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RO water, short for reverse osmosis water, is tap water that has been pushed through a membrane so fine that almost nothing except water molecules gets through. It is the most thorough filtration you can have at home, and it is what most bottled drinking water in Malaysia is made from. This guide explains how it works, what it removes, how it compares with mineral and distilled water, and how to decide whether your household needs it.
Quick answer: what is RO water?
RO water is water forced through a semi-permeable membrane with pores around 0.0001 micron across. Dissolved salts, heavy metals, bacteria, viruses and most chemicals are held back, and what comes out the other side is very close to pure water. Home RO systems add carbon stages before and after the membrane, which is what makes the water taste good as well as test clean.
How reverse osmosis works
Osmosis is what happens when water passes through a membrane from the purer side to the saltier side, which is how plant roots drink. Reverse osmosis uses pressure to push it the other way: from the tap water side through the membrane, leaving the dissolved solids behind.
A home RO purifier does this in four stages:
- Sediment filter
- A PP cotton cartridge catches rust, sand and grit from the pipes.
- Pre-carbon filter
- Activated carbon absorbs chlorine and organic compounds, which protects the membrane and takes away the swimming-pool taste.
- RO membrane
- The 0.0001 micron membrane rejects dissolved salts, heavy metals such as lead and arsenic, bacteria, viruses and microplastics.
- Post-carbon filter
- A final carbon stage polishes the taste of the water as it leaves.
The rejected solids are flushed away to the drain with a small stream of waste water, which is how the membrane keeps itself clear.
What RO removes
| Contaminant | Removed by RO? |
|---|---|
| Chlorine and its by-products | Yes, at the carbon stages |
| Lead, arsenic, mercury and other heavy metals | Yes |
| Dissolved salts and hardness | Yes |
| Bacteria and viruses | Yes |
| Sediment, rust and sand | Yes |
| Pesticides and most organic chemicals | Yes |
| Microplastics | Yes |
| Naturally occurring minerals such as calcium and magnesium | Yes, mostly |
That last row is the trade-off. RO does not know the difference between a harmful dissolved solid and a useful one, so minerals go too. The water is perfectly safe; most of the minerals in a diet come from food, not water. Some people find very pure water tastes flat, which is why post-carbon and mineral stages exist.
RO water vs mineral water
The two are not rivals so much as different answers to different questions.
| RO water | Mineral water | |
|---|---|---|
| Where it comes from | Your own tap, purified | A natural spring or underground source, bottled |
| Minerals | Very low; most are removed | Naturally present, and listed on the label |
| Contaminants | Removed at the membrane | Depends on the source and the bottling |
| Taste | Clean and neutral, sometimes called flat | Varies by source; some taste of the minerals |
| Plastic | None, from a tap | A bottle every time |
Mineral water is chosen for its taste and its minerals. RO water is chosen for what it does not contain. If the question is whether the water from your own tap is safe to drink, RO answers it; mineral water side-steps it. And because most of the calcium and magnesium you take in comes from food, drinking RO water every day does not leave a balanced diet short.
RO water vs distilled water
Distilled water is boiled, and the steam is condensed back into water. That removes almost everything, dissolved gases included, and it is made in batches. RO water comes through a membrane as you need it, keeps a trace of minerals, and tastes more like ordinary water. For drinking and cooking at home, RO is the practical one of the two.
What RO does not do well
- Flow rate
- Water passes the membrane slowly, so many systems store it in a tank to fill a glass at a normal speed. A high-capacity membrane, rated at 600 gallons a day, delivers about 1.5 litres a minute straight to the tap with no tank, which is roughly six seconds for a glass.
- Waste water
- Every litre purified sends some water to drain. Modern membranes waste far less than older ones, but it is not zero.
- Filter changes
- The carbon cartridges last about a year and the membrane about two. A system with old filters is worse than no system, so a filter change reminder is worth having.
- Boiling is not a substitute
- Boiling kills bacteria but does nothing about metals, chemicals or sediment, and it concentrates them as water evaporates.
Do you need RO water in Malaysia?
Tap water in Malaysia is treated to a safe standard when it leaves the plant. What reaches your glass depends on the pipes, the building's storage tank, and the age of the plumbing, which is why the same water can taste and test differently across one city.
RO is worth it if any of these apply:
- The water tastes or smells of chlorine, metal or earth.
- The building is older, or has a rooftop tank you cannot see cleaned.
- There is an infant, an elderly person or someone with a weak immune system in the house.
- You currently carry bottled water home, which RO replaces with water from your own tap.
If none apply, a simpler carbon filter at the tap will improve taste and remove chlorine. Our guide to water purifiers versus water filters explains where that line sits, and our guide to how often to replace a water filter covers the signs that a cartridge is due.
The VATTI One Tap purifier is an RO system
The VATTI One Tap water purifier is a four-stage RO purifier that sits under the sink and feeds a single tap on the counter. The membrane is the 0.0001 micron kind described above, the post-carbon stage handles the taste, and the membrane is rated at 600 gallons a day, so the tap runs at 1.5 litres a minute with no storage tank. A separate heater beside it delivers hot water in three seconds, and the tap gives four temperatures: 100°C for tea, 85°C for coffee, 45°C for a baby's milk, and room temperature. A reminder tells you when a filter is due, and you change the filters yourself by lifting the lid.
RO water FAQs
Is RO water safe to drink every day?
Yes. It is the standard for bottled drinking water and for hospitals. The minerals it removes are ones you get from food.
Is RO water better than mineral water?
Neither is better for everyone. RO water is purer and comes from your own tap; mineral water carries natural minerals and a taste some people prefer. For everyday drinking and cooking, RO water is the one you can have on tap.
Does reverse osmosis remove minerals?
Most of them, yes. That is inherent to the method. It does not make the water unhealthy, and a post-carbon stage brings the taste back.
Is RO water the same as distilled water?
No. Distilled water is boiled and condensed, which removes almost everything including dissolved gases. RO water keeps a trace of minerals and tastes more like ordinary water.
How often does an RO membrane need changing?
About every two years in normal home use, with the carbon filters changed yearly. A drop in flow or a return of the chlorine taste means one of them is due.
Why does RO water taste flat?
Because it is very pure and low in minerals, and minerals are most of what water tastes of. Most people stop noticing within a week, and a post-carbon stage softens the difference.
Final thoughts
RO water is tap water with the dissolved solids, metals and microbes taken out. It is purer than mineral water, more practical than distilled, and the right choice for a household that wants bottled-water purity from the kitchen tap. The VATTI One Tap purifier delivers it hot, warm or at room temperature from one fixture, with filters you change yourself.
