I will be honest about how this started. There is a filter brand that seems to be everywhere right now. Every time I open Instagram or my emails! There they are. Beautiful ads, huge budget, the kind of marketing spend that makes you wonder what it would feel like to have that kind of money behind a launch. I felt a flicker of jealousy watching it, if I am being completely honest.
But underneath the jealousy was real curiosity. Is hard water actually doing what these brands say it is doing to our hair? Or is this another case of a real problem being stretched into a bigger story than the evidence supports? I wanted the actual science, not the marketing version. So I went looking.
What hard water does to hair
Hard water has picked up calcium and magnesium from rock on its way to your tap, usually chalk or limestone. If you live in the South East of England, including London, Hertfordshire, Essex, or Kent, your water is very likely hard. Kent regularly tests as the hardest in the country. Scotland, Wales, and much of the North West have naturally soft water. This is part of why hair can behave differently the moment you travel. It is rarely just the climate. It is often the water.
What we know for certain is that hard water leaves mineral deposits on hair, mainly magnesium, confirmed under a microscope in more than one study. What is less settled is whether this actually weakens the hair. One well-known study found no real difference in strength between hair washed in hard water and distilled water over thirty days, even with visible mineral buildup. Other studies found the opposite, with hard water hair breaking under less force. The honest answer is that minerals reliably build up, but whether that alone breaks your hair depends on how hard your water is and what else you are doing to it. Heat styling and chemical treatments still matter more on their own.
Curly and coily hair tends to feel this faster than straight hair. The more lifted cuticle gives minerals more surface to grab onto, and natural scalp oil already struggles to travel down a coiled strand. So the dryness textured hair already deals with is the same thing hard water makes more obvious, sooner.
The three real solutions
Chelating shampoos contain ingredients built to grab onto mineral ions so they wash out, things like disodium EDTA, tetrasodium EDTA, citric acid or sodium phytate. Where it sits on the ingredients list is a useful clue, since some of these same ingredients are also used in tiny amounts just to stabilise a formula. But position is not proof of concentration. If you want certainty, ask the brand what they actually formulated for.
Our Dúdú Clarifying & Exfoliating Shampoo uses sodium phytate for exactly this reason, positioned well ahead of the preservatives in the formula. Used well, chelating shampoos are genuinely effective for clearing buildup, best now and then rather than every wash since they can be drying.
Apple cider vinegar and other acidic rinses are mildly acidic, and hair sits happiest slightly acidic too, around pH 4.5 to 5.5. At a lower pH, the cuticle scales lie flatter against the strand rather than standing raised, which gives that smooth, shiny feeling after a rinse. What ACV does not have good evidence for is actually removing hard water minerals. The smoothing is about pH, not mineral removal. That is likely why it feels amazing once, and then the same problem returns within a week. You smoothed the surface. You did not clarify what is underneath it.
Shower filters and water softeners are the only options that deal with the water itself rather than the hair afterward. A filter reduces some mineral content but will not fully soften water. A softener removes calcium and magnesium before it reaches the tap, the most thorough fix and also the most expensive.
So which one is actually best
It depends on how hard your water is and how much buildup you already have. For mild dullness or dryness, a chelating shampoo every week or two is a sensible, evidence-backed first step. If you are in a genuinely hard water area like London or Kent and breakage does not improve no matter what you wash with, a shower filter is worth it, with a full softener as the most effective option if budget allows.
What is not worth doing is buying something just because the word chelating appears on the label. The science behind chelation is solid. Not every product claiming to do it actually delivers it in a meaningful amount.
And about that filter brand. The marketing might be bigger than the science behind some of their specific claims. But the underlying problem they are selling against is real, even if not every solution on the market fully backs up what it promises.
