From sea to drinking water – purification step by step
The technology used in MAB watermakers is reverse osmosis (RO). This is the same technology used in hospitals, laboratories, and municipal water treatment plants worldwide. Today, RO is the most reliable method for producing drinking water from both seawater and brackish water.
What happens in the actual process?
Pre-filtration
The water first passes through mechanical pre-filters (20 µm → 5 µm). These remove sand, particles, algae, and other contaminants visible to the naked eye.
High pressure & membrane
The water is then forced through the reverse osmosis membrane. The membrane is extremely fine, with pores around 0.0001 micrometers. This is so small that:
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Salt ions are blocked
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Bacteria and viruses are thousands of times too large to pass through
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Heavy metals, microplastics, organic substances, and other dissolved contaminants are rejected and flushed back to the sea
What passes through is essentially only water molecules, which are then routed to the fresh water tank.
Important to understand
Reverse osmosis is not a conventional filter. Without pressure, no purification takes place.
In reverse osmosis, water is forced through a semi-permeable membrane at a pressure exceeding the water’s natural osmotic pressure. This allows water molecules (H₂O) to pass through the membrane structure, while salt ions and other dissolved substances are retained.
It is therefore a pressure-driven separation at the molecular and ionic level – not a sieve that simply “filters out dirt.”
The substances that do not pass through are discharged as concentrate (brine), which is why all RO systems always produce wastewater.
In practice, RO membranes remove
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99.5–99.9% of salts
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99.99% of bacteria and viruses
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99%+ of heavy metals and organic contaminants
The remaining “fractions of a percent” are not harmful residues passing straight through. They are extremely small trace elements and mineral ions found in virtually all drinking water – including municipal tap water.
RO water from a watermaker is often cleaner than many bottled waters.
Confidence in numbers
Water produced by MAB systems should have:
TDS (Total Dissolved Solids) below approximately 500 ppm
(typical drinking water is usually in the range of 50–300 ppm)
With seawater, results typically fall between 150–350 ppm depending on salinity, temperature, and membrane condition.
To put this into perspective:
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EU drinking water limit: 1,500 ppm
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Water starts to taste salty: >700 ppm
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Typical MAB results: 120–300 ppm
This is not “2% contamination slipping through.”
It is normal drinking water with trace mineral ions – just like all other drinking water.
Why is RO so reliable?
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It is a physical barrier – no chemicals are involved to reduce effectiveness
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The membrane simply does not allow molecules larger than water to pass
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The technology is standard in medical care, food production, and the space industry
As long as the TDS values are correct, you know the system is working as intended.
Filters and membranes – what maintenance is required?
Pre-filters:
Replace when they become brown, clogged, or develop odor. In practice, this means every 3–4 weeks during active use, or once per season otherwise.
Membrane:
Typically lasts 2–5 years depending on water temperature, feed water quality, and how frequently the system is flushed.
TDS meter:
A simple instrument that immediately shows how well the purification is working.
If the TDS value is normal, the membrane is healthy.