What a shower filter can — and cannot — do

July 29, 20263 min read

Falling shower water photographed in cool natural daylight.

Search for a shower filter and you will find twenty-stage cartridges, lists of a dozen contaminants, and before-and-after photographs of hair. Very little of it tells you how the product actually works, and almost none of it tells you under what conditions the numbers were measured.

So here is the plain version.

What an inline shower filter is

A filtered showerhead sits between your shower arm and the water leaving the spray face. Water passes through a replaceable cartridge on its way through. That is the whole mechanism. It treats the water going through that one fixture, at that one moment, and nothing else in your home.

What this category is actually recognised for

There is an industry standard specifically for this product type: NSF/ANSI 177, Shower Filtration Systems — Aesthetic Effects. It exists to certify one thing in particular: reduction of free available chlorine. That is the claim the standard was written around, and it is the claim you should look for when a manufacturer says a shower filter is certified.

Note the word aesthetic. The standard addresses the taste, odour and feel side of water quality. It is not a health-effects standard, and a certification under it is not a medical claim.

What varies, always

Three things determine what any shower filter does in your bathroom, and none of them are printed on the box.

Your water. Municipal water differs by city, by season and sometimes by street. A filter tested against one water profile will behave differently against another.

How much water has gone through it. Filter media are consumed. A cartridge on day one and the same cartridge on day eighty are not the same product. This is why a stated capacity matters more than a stated percentage.

Flow and temperature. Contact time between water and media changes with flow rate. Hot water behaves differently from cold. A number measured under one set of conditions does not transfer to another.

This is why we are uncomfortable with percentage claims presented without their conditions. A figure like "reduces 99% of chlorine" is close to meaningless unless you also know the water, the flow rate, the temperature and the volume at which it was measured.

What a shower filter is not

It is not a water softener. Softening is a different process, addressing different minerals, usually at the point where water enters the building. A filter on one showerhead does not soften your home's water and should not be sold as though it does.

It is not a medical device and it is not a treatment. If you have a persistent skin or scalp condition, that is a conversation with a doctor or dermatologist, not a purchase decision.

It is not a substitute for your water utility's treatment. In the EU, drinking water quality is regulated under Directive (EU) 2020/2184, and in Sweden it is overseen by Livsmedelsverket. Your tap water is already treated to a legal standard before it reaches you.

Where that leaves VANNR ONE

We are developing a filtered showerhead. We think there is a real, modest, worthwhile thing this product category does. We also think the category has been oversold to the point where a customer cannot tell a tested claim from a marketing sentence.

So we are not publishing reduction figures for VANNR ONE yet. We do not have independent test results for the finished production configuration, and until we do, anything we said would be a supplier's claim wearing our logo.