I spent eleven months and about £400 trying to fix my hair. The problem was coming out of the wall.

It started with the plughole. I'd washed my hair, same as every other morning. Then I crouched down to clear it out, and what came away in my fingers was too much.

I knew it was too much because I had been keeping score for months without once admitting that was what I was doing.

You don't decide to start counting. You just find yourself doing it. Holding the wet clump flat against your palm. Spreading it a little with your thumb. Working out whether it's more than last time, knowing perfectly well that it is. It always weighs less than you expect and looks like more than you can bear. And then you tell yourself you're being dramatic, and you rinse your hand under the tap and watch it go, and you get on with the morning, because it's twenty past seven and the baby is awake.

I did that most weeks for the better part of a year.

I never said this next part out loud to anyone.

For a long time I had a story I told myself about it. Stress. The move. A bad few months. Something that would sort itself out once everything else settled down.

The trouble with that story is that everything else did settle down, and this kept going, and got worse while it did. So one evening I was standing under the bathroom light, the horrible bright one, tilting my head to see my parting properly, with no story left to tell myself. And I could see scalp at my temples. Not a patch. Just more scalp than there used to be, in a place where there had never been any.

I typed a sentence into a forum at midnight and deleted it twice before I let myself post it: no bald patches, but I feel like I'm not far from it.

I was thirty-four.

I find it slightly humiliating to be writing several hundred words about my own hair. It is hair. Nobody is ill. I have a toddler, a mortgage and a job.

But I spent eleven months and about £400 trying to fix something that turned out not to be broken, and I would like the next woman to skip that part.

The problem was not my hair. It was not my hormones, my shampoo, or my hairdresser. It was coming out of the wall, and it had been doing it every single morning for eleven months. Once I knew what it was, sorting it took two minutes. I'll get to what, and how.

The cupboard under the sink

I should tell you what "doing everything right" had cost by then, because I think the number matters.

Fourteen products in eleven months. The bond-repair treatment everyone was posting about, then the second one in the range, then the whole set, because obviously if it isn't working you haven't bought enough of it. A £32 shampoo the hairdresser suggested. Two salon masks, one of which I still have and cannot throw away. A scalp serum with a pipette, applied nightly, religiously. A pre-wash oil. A silk pillowcase. Supplements, three months, taken with breakfast so I wouldn't forget. A clarifying shampoo. Then a chelating shampoo, when the clarifying one did nothing, because a forum told me chelating was the serious version.

And somewhere in the middle of all that, I started doing a final rinse with water from the dehumidifier.

I want you to sit with that one. I stood in my own bath, pouring a jug of water I'd collected out of a machine in the hallway over my own head, because I had run out of anything else to try.

The cupboard under my bathroom sink, by the end, was a museum of things that were supposed to be the answer. Every bottle half used. I couldn't throw any of them out, because throwing them out felt like admitting the whole eleven months.

And my hair got worse in three directions at once.

It snapped. Not fell, snapped: short pale broken pieces on my shoulders, in the sink, across the back of every dark jumper I owned, and ends that felt like dry grass when I pulled them through my fingers. My scalp was tight and itchy all the time and worse after a wash, which made no sense to me at all, because washing your hair is supposed to be the thing that helps. And it was thinning at the front, in the exact place you notice first and mention last.

I got very good at the low bun. It stopped being a style and became camouflage.

The photograph

The breaking point wasn't the mirror. You can manage a mirror. You look at the bits that are fine and you angle away from the bits that aren't, and you do it so automatically you don't notice you're doing it.

It was a photo somebody else took, at a christening, from behind and slightly to the side, the angle you never see yourself from. My hair in it looked thin in a way I had been telling myself it wasn't. And the thing that actually did it, the thing that made me put the phone face-down on the table, was that this photo was from after. After the bond-repair set, after the serum, after the eleven months and the £400 and the dehumidifier water.

The direction of travel was still down. With everything.

That was the night I stopped searching for products and started searching for reasons.

The nine seconds

Four weeks later I was in the chair for a cut. My hairdresser, who I've known about a year, since we moved, was combing through the ends when she stopped and said, half to herself, that they were awfully dry at the bottom.

I said something about how they'd been like that for months, and that I'd tried everything.

Then she asked where we'd moved from. I said west, near my mum's.

"Ah," she said. "Right. That'll be it, then."

I asked her what she meant.

"I can usually tell," she said, "which side of the county someone lives on. By how the colour takes, mostly. And by this." She ran the ends through her fingers again. "People move over here in the spring and they're sat in that chair by autumn saying more or less exactly what you said when you sat down."

Which was: nothing works on it any more.

Then she said it plainly, the way you'd tell someone their headlight was out.

"It's not your hair, love. It's your water."

I want to be honest about my first reaction, because it wasn't gratitude. It was a sort of tired scorn. I had heard "have you tried" about forty times by then and this sounded like number forty-one.

But she wasn't quoting a study at me and she wasn't selling me anything. She washes forty heads of hair a week in this water and she'd noticed a pattern.

The last thing she said, wringing out a towel and not really looking at me, was that it puts a coat on. A bit of it every wash, day after day. The daily coat is the phrase she used, and it's the one I've used ever since.

I got home and did a lap of my own house like a woman looking for something she'd lost.

The kettle first, because it's the one everybody knows. Furred white inside, and I descale it, and it comes back. Then upstairs: the shower screen that goes cloudy four days after I clean it. The showerhead with a crust on it that I chip off with my thumbnail when I can be bothered.

I had been looking at all of that every single day for eleven months and I had never once connected it to the thing happening on my head.

So I did what I imagine you'd do. I decided the answer was hard water, because hard water is the thing everyone talks about, and I started pricing up a softener. Two quotes. A thousand pounds, then thirteen hundred, plus a salt tank in the cupboard under the stairs and a conversation with a landlord I did not fancy having.

I spent about a month saving for that machine before I found out it wouldn't have fixed what was actually wrong.

Hard water and chlorine are not the same thing

What made me willing to read the chemistry at all came before any of the chemistry.

On a Mumsnet thread about hard water, a woman described washing her hair on a holiday in Cornwall and "couldn't believe... my hair was so soft and swishy."

She had changed nothing. Same person, same hair, same bottles in the same wash bag. The only variable was what came out of the wall.

Water is a variable. It has contents of its own, and those contents end up on your head every day whether you think about them or not. Nobody had ever put that in front of me.

So I went and found out what was actually in mine. It took me a week of reading to get straight, mostly because I had two different things filed under one heading. Separated out, which is the bit nobody had ever done for me:

That was the month I lost. I'd heard "it's your water", filed it under hard water like everybody does, and started saving for the machine that deals with hard water. It was the other one.

The half you can see, and the half you can't

Go and look inside your kettle in a minute. I want you to know what you're actually looking at when you do.

That white crust is the mineral half. The visible half. It's what your water leaves behind on a surface once the water itself has gone.

The crust is not your enemy. It's your evidence. It's proof that the water coming into your house doesn't arrive empty, that it's carrying a load, and that it puts that load down on whatever it touches and then dries.

And this is the part that got me. The chlorine came in with it and left no mark at all.

It was there. It just doesn't leave crusts. It's the half you can't see: nothing to scrape off with a thumbnail, nothing to photograph and put in a forum post, no white ring to point at.

So the harmless half is the one that announces itself all over your house, and the half that's actually doing something to you is the one that goes through completely silently.

Which is exactly how I spent eleven months auditing my shampoo and a month pricing a machine that would have scrubbed the visible half off my kettle and left the invisible half running every morning.

Same with the window, if you've ever cleaned one in a hard water area. Right product, right cloth, no streaks at all while it's wet, and it still dries with a haze on it. That haze is what the water left, not dirt you failed to get off.

That's the minerals. And whatever else was dissolved in that water went on the glass at the same time, it just didn't leave a mark.

Now put your head where the window is.

What lands on you, every single morning

When shower water hits your hair and skin and dries, a thin layer of what was dissolved in it stays behind. Deposited, not rinsed. On the strand, on the scalp, on your face. That's the daily coat, the thing my hairdresser named while she was wringing out a towel.

And the bit that reorganised eleven months of my life in about four seconds is that a fresh coat goes down tomorrow morning. And the morning after that, and the one after that. Every wash lays a new one.

So every mask, every serum, every expensive thing I was putting on at night was going on top of a fresh coat that got laid down again before I'd had my coffee.

My £32 shampoo had been working the whole time. It was working on a surface I was re-coating every morning, for free, in my own bathroom, at seven o'clock.

So which half is actually doing the damage

This is the question I sat down and answered properly, and the answer is the reason I did not buy the softener.

The calcium is the boring one. It furs up the kettle, it clouds the screen, it's the reason I'd been getting quotes. It is a nuisance made of limescale.

The chlorine is the one doing something to you.

Two things, and once I understood them I couldn't unsee either.

Your hair is made of keratin, which is a protein, and chlorine is an oxidiser. That's its whole job. And oxidisers are hard on proteins. It roughens the outside of the hair shaft and makes it brittle, so it snaps instead of bending. It's the same reason a swimmer's hair goes to straw by August. Your shower is far weaker than a pool, which is why nothing happens on Tuesday. But you are not in a pool every morning for a year. You are in this.

Your skin makes its own oils, and those oils are what hold water in. Chlorine strips them. There's published work on it: free residual chlorine measurably reduces the outer layer of skin's ability to hold onto water (Seki and colleagues, 2003). Strip that barrier every morning and you get tightness, dryness, and skin that never quite settles.

And your scalp is skin. That was the bit I had never once thought about. For eleven months I'd treated my scalp as the thing hair comes out of, rather than as skin that was getting stripped every morning like the rest of me.

There's a second piece of research worth knowing, because it explains the products. Danby and colleagues, 2018, found that washing in hard water leaves more of your shampoo behind on your skin rather than rinsing clean. So the mineral half doesn't attack you, it just makes sure everything else sticks around longer than it should.

Put together: the chlorine strips, the minerals make the residue cling, and both of them arrive again tomorrow.

That was the answer to the question I'd been asking for eleven months. Nothing was wrong with my hair. Something was being done to it, every single morning, by the one ingredient I had never thought to question.

And chlorine is the half you can actually do something about without ripping your bathroom out.

The part I'm still annoyed about

Once you see it you cannot unsee it, and what arrives first is relief and anger at the same time, which I hadn't expected.

Relief because it was never me. I wasn't using them wrong. My hair hadn't mysteriously stopped responding. My body wasn't broken.

Anger because I have spent my entire adult life being sold products for my hair and my skin, and every single one of them assumes the water is neutral. Not one label, not one salon, not one article in eleven months of frantic searching told me to audit the input. The whole industry is built on auditing the output.

What I actually bought, and what it doesn't do

The fix, once you understand the problem, is almost boringly obvious: treat the water before it touches you, rather than treating your hair after the water already has. Which means it has to happen in the last few inches, inside the shower head itself. You take your old head off. You put a filtered one on. That is the entire intervention. Solace call it pre-contact filtration, which I assumed was marketing-speak until I understood that the "pre" is the whole point, everything else in my bathroom was post-contact.

Three stages inside it, each doing one job, which I liked, because "purifies your water" is exactly the kind of sentence that had been taking my money all year.

• A copper-zinc medium called KDF-55, which is the one that matters. The media itself is certified to NSF/ANSI Standard 42, and it takes out over 95% of the free chlorine, and it does it at shower temperature, which is not a given. Ordinary carbon filters fall over in hot water, and nobody showers cold.
• Then calcium sulfite, which backs up the KDF-55 and catches whatever gets past the first stage.
• Then coconut activated carbon, which pulls the organic compounds and the chlorine smell most of us have mistaken our whole lives for "clean."

So the thing arriving every morning that was roughening the hair shaft and stripping my skin: over ninety-five per cent of it, gone, before the water gets anywhere near me.

Now the part I want to be very clear about, because this is the exact thing that stopped me buying a filter twice before.

It does not soften your water. Not in the real sense. Softening means ion exchange, which is the thousand-pound machine I'd been quoted for. No shower head can do that, including this one. Anybody telling you theirs softens water is either confused or hoping you are. If you've read that on a box and thought that can't be right, you were right. I checked the small print on two of them for exactly that reason and put both back.

I would rather be the one telling you this than the one you catch.

What it does instead is stop the chlorine, and the trace metals like copper and lead that ride along in mains water, reaching you at all.

And this is what I wish somebody had told me while I was saving up for a softener. A softener wouldn't have fixed this either. Ion exchange pulls out the calcium and the magnesium. It does not touch chlorine. So the thousand pounds I was putting aside would have sorted my kettle and my shower screen, and left the thing that was actually oxidising my hair every morning exactly where it was.

A month of saving for the wrong machine, on top of eleven months of buying the wrong bottles.

I'll be equally honest about the other objection, because it was mine: is this just hype? I had already been burned by a fifteen-quid one from a marketplace that I genuinely could not tell was there. So the reason I bought this particular one wasn't the copy on the page. It was the returns terms, which I read twice because I assumed I'd misread them the first time. A hundred days, and the reason it's a hundred rather than a round thirty is that a cartridge lasts about ninety. They've given you a full one, plus a fortnight to make your mind up. Fitted, used, run for months, any condition at all, and you can still send it back for your money. A year's warranty on the unit on top.

And the maths, once I finally did it properly, was not close.

A thousand pounds for the machine that would have fixed my kettle and left the real problem running. Four hundred a year for the cupboard that fixed nothing. A hundred and fifty for the one thing that changed what came out of the wall.

I'd spent a fortnight reading the small print on things like this by then, and the small print is always where the number goes quiet: the window is generous and the condition is not. So read theirs, whoever you end up buying from. Read the condition, not just the number. That's the whole trick of it.

What I can tell you, and what I won't

This is the part where an article like this one usually starts lying to you, so let me be careful.

What I can tell you is what it does. From the first wash, the chlorine and the dissolved metals stop arriving on my head. That's simply what filtration is, and it happens whether I notice it or not. It isn't a feeling and I'm not offering it as one.

What I won't tell you is that it happened overnight. It didn't. There was no morning where I stood in the shower and knew. If I told you there was, you should close this tab, because that is what every bottle in that cupboard promised me.

What there was instead was a slow turn, in this order.

Month three was the bit that made me angry all over again. There had never been anything wrong with the products. I had been putting good things on top of a surface that was being stripped every morning, and then blaming the good things.

I want to be careful here, because I know what some of you are reading this for. I never had eczema. I've never been diagnosed with anything, never been to a doctor about my scalp, and I can't tell you the first thing about whether any of this is relevant to somebody who has. It wasn't a condition. It was an itch I'd stopped noticing I had, and then one day I noticed it wasn't there.

There's one more thing I didn't expect, and I'll flag it because it might matter more to you than it did to me.

It isn't only your hair. The hair thing and the skin thing are two different mechanisms, and I'd only been paying attention to one of them.

The hair one is the oxidiser roughing up a protein. The skin one is separate: chlorine strips the oils your skin uses to hold water in. And it does that everywhere the water lands, every morning, not just to the bit with hair growing out of it. Your face. Your back. Your legs in winter. The scalp I'd spent eleven months treating as a hair problem and never once as skin.

So if your skin has been doing something you can't account for, and nobody has ever been able to tell you why, and you've been going at it from the outside with creams the way I was going at my hair with masks, then it is at least worth knowing there's a daily stripping event in your routine that nobody ever told you to look at.

I can't tell you it's your answer. Nobody honest could. But I'd spent eleven months not knowing the question existed, and I'd rather you had it.

Six months on, the cupboard has stopped filling up. I use three things. I don't stand in Boots at half eight reading the back of a box any more, and I don't do the maths in the shower.

So no, nothing announced itself. It stopped getting worse, and then it slowly went the other way, in the order above.

I gave it a full cartridge before I decided, which is three months, roughly a third of the time it took for all of this to go wrong in the first place. A problem eleven months in the building does not get undone by Thursday. Anybody who tells you otherwise is trying to sell you the twelfth bottle.

The one practical thing, because someone will ask: it isn't permanent-and-forget. The media inside gets used up, that's what used up means, it's holding what it caught, so it's a new cartridge about every three months. You change it on the calendar, not on a feeling. Which is also why I bought the year in one go rather than the single. Same reason you don't buy one toilet roll.

So, no moment, but not nothing either. What there is instead is a stressor that turns up every morning and then doesn't, for a hundred days, in your own bathroom and on your own hair, with the option to send the thing back afterwards in whatever state it's in.

This is the version of it I'd have wanted to picture, back in January.

It's an ordinary Tuesday morning, some months from now. You get out of the shower and you don't crouch down at the plughole. Not because you decided to stop. Because it stopped being the thing you do.

Somebody takes a photograph at somebody else's christening, from behind and slightly to the side, and sends it to the group chat. You look at it properly. You don't put your phone face down on the table.

After the year I'd had, that was the only version of this I was ever going to believe. Not a promise about how my hair would feel by Friday, but a change to the input and enough time for it to count, on terms where being wrong cost them instead of me.