The question that follows “it keeps the minerals” is always the same one: then what does it take out? It is a fair question, and the answer is that the CDI chamber is the heart of a Biofier, not the whole of it. There are ten stages. Each has one job.
Before the water reaches the cell
The first stages are protective. Sediment filtration catches suspended particles, the silt and rust that cloud a glass. A microbe-deactivating filter neutralises bacteria, viruses and other microorganisms, which is the safety case that made RO the default in the first place. Activated carbon removes chlorine, unpleasant odours, organic impurities and the compounds that make water taste and smell wrong, and reduces traces of certain heavy metals and chemical contaminants along the way.
By the time the water reaches the CDI chamber, the biological and organic work is done. What remains is the dissolved, invisible load: salts and ions.
What the CDI cell does
Capacitive deionisation is an electrochemical process. As water flows between porous electrodes carrying a low voltage, dissolved ions are attracted to the oppositely charged surface and held there. Excess sodium, chlorides, dissolved salts, nitrate and other undesirable charged contaminants are captured on the electrodes rather than pushed through a membrane under pressure.
The control is the point. Intelligent control of the electrical field is what lets the system reduce the unwanted dissolved impurities while retaining beneficial minerals such as calcium and magnesium at desirable levels — the same selectivity the technology was developed for in large-scale desalination.
How it cleans itself
Electrodes fill up. When they reach their adsorption capacity, the polarity is reversed, the captured ions are released into a reject stream and flushed away, and the electrodes are regenerated for the next cycle. That is the Auto Clean you see on the product. No membrane to replace on a schedule, no chemicals, and it is a large part of why five years of maintenance can be included in the price.
After the cell
Stored water is protected by a UV LED — Germ Shield — so the litres waiting in the tank stay as protected as the litres that were just purified, and the spout is designed to keep insects out.
What that adds up to
- Microbes, chlorine, odour and particles handled before the cell.
- Dissolved salts, sodium, chloride, nitrate and charged heavy-metal ions captured by the cell. In the IAPMO testing, nitrate came out at a fraction of the permitted limit in every condition.
- Calcium, magnesium and bicarbonate largely left where they were.
- Up to 70% of the incoming water recovered for use rather than sent to the drain, validated by IAPMO with a 5-star water-saving rating.
Removing the bad, retaining the good. That is the whole design, and it takes ten stages to do it properly.
