Why CARA Uses Two Filters in the RO Water Station
Reverse osmosis is recognised as one of the most effective ways to reduce a broad range of unwanted substances from drinking water. But because the process is so thorough, it often raises an important question:
Does reverse osmosis also remove healthy minerals—and if it does, should you be concerned?
The short answer is yes: reverse osmosis reduces naturally occurring dissolved minerals, including calcium and magnesium, along with many unwanted dissolved substances.
However, that is only part of the story.
The contribution drinking water makes to your mineral intake varies according to your local water supply, while food remains the principal source of essential minerals for most people. Some reverse osmosis systems, including the CARA CA3001, also include a final mineral-enhancement stage that adds selected minerals back into the water after purification.
Let’s look at what really happens—and clear up some common confusion.
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What Does Reverse Osmosis Remove?
Reverse osmosis, commonly shortened to RO, works by passing water through a very fine, semipermeable membrane.
The membrane separates many dissolved substances from the water, helping reduce contaminants and impurities that may be too small for standard sediment or carbon filters to address effectively.
Depending on the system and water conditions, reverse osmosis may help reduce:
- Fluoride
- Lead and other heavy metals
- Chlorine and chlorine by-products
- Nitrates
- PFAS and PFOS
- Microplastics
- Dissolved salts
- Sediment and fine particles
- Bacteria and viruses
- Naturally occurring dissolved minerals
The RO membrane does not decide which dissolved substances are “good” and which are unwanted. It is designed to provide broad-spectrum purification, so it reduces many substances according to their molecular size, charge and other characteristics.
You can learn more about the process in our guide, Why Reverse Osmosis?
Does Reverse Osmosis Remove Calcium and Magnesium?
Yes. Reverse osmosis can reduce naturally occurring calcium and magnesium from water.
These minerals contribute to what is commonly referred to as water hardness. The amount present in tap water can vary considerably between different Australian water supplies.
Calcium and magnesium are essential nutrients, but the fact that RO reduces them does not automatically mean the resulting water is nutritionally inadequate.
The more useful question is:
How much do we normally rely on drinking water for our mineral intake?
Do We Get Most of Our Minerals From Water?
Drinking water can contribute to calcium and magnesium intake, particularly in areas with mineral-rich or hard water. However, the amount varies significantly depending on the water source and location.
The World Health Organization notes that food is the principal source of both calcium and magnesium, although drinking water can make an additional contribution.
Most people obtain magnesium through foods such as:
- Leafy green vegetables
- Legumes
- Nuts and seeds
- Wholegrains
Calcium is also found in a wide range of foods, including:
- Fortified plant milks
- Tofu set with calcium
- Tahini and sesame seeds
- Almonds
- Leafy green vegetables
- Legumes
- Dairy products for those who consume them
Healthdirect advises that most people obtain the magnesium they need from food, although the amount in drinking and bottled water varies.
This does not mean the minerals naturally present in water are worthless. It simply means drinking water is generally one part of a much larger nutritional picture.
If you have a diagnosed mineral deficiency, a restricted diet or concerns about your nutritional intake, it is best to discuss these with a qualified healthcare professional rather than relying on drinking water alone to meet your needs.
Does Low-TDS Water Mean It Has No Value?
No. A low Total Dissolved Solids reading does not mean that water has no value or that it is automatically unhealthy.
TDS measures the combined quantity of dissolved substances in water. These may include calcium, magnesium, sodium and potassium, but also salts, metals and other dissolved material.
A TDS meter gives you a number—it does not identify each substance or tell you whether it is beneficial, harmless or unwanted.
This is why a high TDS result does not necessarily mean water is unsafe, and a low result does not independently prove that water is free from every possible contaminant.
TDS is useful for observing the overall reduction in dissolved substances achieved through reverse osmosis, but it should not be treated as a complete water-quality assessment.
Read our detailed explanation: What Is TDS in Water—and Why Does It Matter?
Why Are Minerals Added Back After Reverse Osmosis?
Some people find that highly purified RO water tastes different from the water they are accustomed to drinking.
Taste is influenced by several factors, including the minerals and dissolved substances present in the water. Adding selected minerals after RO filtration can create a smoother, more balanced and enjoyable drinking experience.
Remineralisation may also gently influence the pH of the finished water, depending on the system, mineral media, incoming water and operating conditions.
Importantly, remineralisation occurs after the main purification process. This allows the RO membrane to first reduce a broad spectrum of dissolved substances before selected minerals are reintroduced.
It is a two-part approach:
- Purify the water
- Enhance the finished water with selected minerals
