Hard water and chlorine are not the same thing

A great deal of shower-filter marketing treats hard water and chlorine as one problem with one solution. They are not, and conflating them is how people end up buying the wrong product.

Hardness is minerals

Water hardness is a measure of dissolved calcium and magnesium. It comes from the geology the water has passed through, which is why hardness is a regional characteristic — two cities on the same national grid can have very different water.

The World Health Organization has published a background document on hardness in drinking water as part of its Guidelines for Drinking-water Quality. The short version: hardness is not considered a health concern at the levels normally found in drinking water. It is a practical and aesthetic issue — limescale on fixtures, more soap needed to lather, a particular feel on skin and hair.

Crucially, hardness is not removed by filtration in the way people assume. Reducing hardness means softening, usually by ion exchange, usually installed where water enters the building. A cartridge inside a showerhead is not doing that, whatever the packaging implies.

Chlorine is a disinfectant

Chlorine is not a contaminant that got into your water by accident. It is added, deliberately, because it works. Disinfection of drinking water is one of the more consequential public health measures of the last century, and the residual you can sometimes smell is evidence the system is doing its job all the way to your tap.

Chlorine is also the thing shower filters are genuinely designed around. NSF/ANSI 177, the standard for shower filtration systems, is built around free available chlorine reduction. If a shower filter has a credible certified claim, this is usually it.

Why the distinction matters when you are buying

If your complaint is limescale on the glass and a film on fixtures, that is hardness, and a showerhead filter is not the answer. If your complaint is the smell of the water and how it feels during the shower, that is more likely chlorine, and this product category is at least aimed at the right target.

A product that promises to solve both is either describing two different technologies in one housing, or is not being precise. Ask which.

What we will and will not say about VANNR ONE

We will not describe VANNR ONE as a water softener, because it will not be one. We will not publish a chlorine reduction figure until the finished production configuration has been independently tested, because the figure would otherwise be someone else's, measured on someone else's product.

When we have a result, we will publish it with the conditions attached: the laboratory, the protocol, the water, the flow rate and the volume. A number without its conditions is decoration.

Sources

• World Health Organization, Hardness in Drinking-water — background document for the Guidelines for Drinking-water Quality
• World Health Organization, Guidelines for Drinking-water Quality
• NSF/ANSI 177: Shower Filtration Systems — Aesthetic Effects
• Directive (EU) 2020/2184 on the quality of water intended for human consumption