Remineralised water is not the same as water that kept its minerals

Most premium RO purifiers sold in India now include a mineral cartridge. The pitch writes itself: it removes everything harmful, then puts the good things back. Best of both worlds.

It is a reasonable engineering response to a real problem. It is not the same as never having removed them.

What a cartridge actually does

A remineralisation cartridge is a small chamber of mineral media — typically calcite, magnesium oxide, or a blend — that the purified water passes over on its way out. Some of that material dissolves into the water.

So the water leaves with minerals in it. But it is a different set, in different proportions, from a different source than the ones removed a few centimetres earlier.

Three ways they differ

• Composition. Groundwater carries a complex profile shaped by the rock it moved through — calcium, magnesium, potassium, bicarbonates, sulphates, trace elements. A cartridge adds a short list.
• Consistency. Cartridge output changes as the media depletes. Fresh cartridge, generous dose. Six months on, considerably less. You cannot see this happen.
• Status. Under Indian food standards, minerals added to water are an ingredient. They are certified, invoiced and batch recorded. Minerals that were never removed are simply part of the water.

Does that make it bad water?

No. A remineralised RO is better than an RO without a cartridge, and the manufacturers who fit them are responding to a genuine shortcoming rather than inventing one.

But it is worth seeing the shape of what is happening. The water is stripped and then partially reconstituted, and you are asked to accept the reconstitution as equivalent. Sometimes it is close. It is not the same.