Percy's Panorama What's In The Water

There's a paddling pool at our training venue in Brasted.

This time of year it sits outside, filled by hose, open to the sun and the air, quietly collecting the contributions of every dog who's been in and out of it over the course of a session.

By mid-morning it looks, frankly, worse for wear — nowhere near as inviting as the fresh water bowl sitting right beside it. Clean. Clear. Topped up regularly. To a human eye, it's not even a contest.

The bowl wins on looks every time.

We dogs, unfortunately, never got the memo.

We drink from the pool. Lots of us, repeatedly, and in clear preference over the bowl. For a while everyone chalked this up to the obvious explanation — the pool's bigger, drinking from it is more of an event, maybe the depth suits us better. Reasonable guesses. I've come to think they're also wrong.

Here's what's actually happening in that paddling pool.

Big surface area, sitting in the sun, agitated by a hose as it fills — which happen to be close to perfect conditions for chlorine to evaporate straight out of the water. That's not a guess, it's chemistry: it's exactly why people with fish tanks leave tap water standing before they add any fish to it. So the pool, baking in the afternoon and getting churned up by hose and paws, may well be carrying a lot less chlorine than the bowl that just got poured fresh beside it.

The bowl the humans think is clean, we're turning down. The pool the humans think is questionable, we're choosing. The whole idea of what counts as "good water" has been quietly flipped on its head — and the thing that did the flipping is my nose.

Then there's a second thing I've noticed at the same venue. Some dogs — not all, but enough that it's a pattern — won't touch the water bowl at all. They wander over, have a proper sniff, and walk away.

Their owners write it off as fussiness, that stubborn quirk we get filed under "personality" instead of what it probably is: communication. I've stopped assuming it's fussiness.

A dog standing at that bowl is running somewhere in the region of 300 million scent receptors. You're working with about six million.

My brain hands over roughly forty times more real estate to smell than yours does. We can pick up chemicals at concentrations measured in parts per trillion — some of us get trained to sniff out cancer, predict seizures, detect certain viral infections, find water and gas leaks under ground (probably pretty lucrative business right now I may consider a career change) find bodies underwater, and yes, underwater, because anything with dissolved chemicals in it is basically a book we can read through the water itself.

Truly pure water — the distilled stuff — doesn't smell of anything at all. Tap water isn't pure. It has a chemical signature, and I'm reading it in the couple of seconds before I decide whether it's worth drinking.

You assess water mostly with your eyes and your tongue. Your eyes pick up clarity and colour, neither of which tells you much about what's actually dissolved in there. Your tongue isn't much better placed — you've got around 9,000 taste buds to my 1,700, so credit where it's due, your palate is the more sophisticated instrument. But even that richer palate tells you almost nothing about dissolved disinfectants, coagulant residue, or pesticide traces at low concentrations. Which means that, in this one specific situation, you're the species with the worse detection kit confidently overruling the one with the better kit.

And the better kit gets called fussy for its trouble.

That's the case I want to make.

What follows is me taking seriously something the dogs at that venue already seem to know.

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Let's get into the facts, because there are real ones here and they don't need any help from me to be alarming.

In September 2024, the Drinking Water Inspectorate — the government body that regulates drinking water quality in England and Wales — served South East Water with a formal Regulation 28(4) notice over Pembury Water Treatment Works, which supplies Tunbridge Wells and the surrounding area.

In its own words, in a publicly available document, the Inspectorate found

"a significant risk of supplying water... that could constitute a potential danger to human health or could be unwholesome."

One of the specific problems named, and formally required to be fixed: pesticide levels entering the raw water reservoir. The deadline South East Water has been given to sort that out is May 2031.

Then, in November 2025, 24,000 homes across Tunbridge Wells, Pembury, Frant and Eridge lost their water supply completely, after a batch of coagulant chemicals was wrongly introduced into the treatment process.

A boil water notice went out.

The Drinking Water Inspectorate opened a formal investigation.

A second major incident, this time across the wider Kent and Sussex supply area, was declared in January 2026. South East Water is currently under a Section 18 enforcement order for Pembury Water Treatment Works, and a separate, company-wide enforcement notice covering discolouration risk across their whole supply area doesn't even conclude until April 2035.

None of that is me speculating. It's all publicly documented on the Drinking Water Inspectorate's website — links at the bottom of this piece if you want to check it yourself. I'm laying it out plainly because it doesn't need dressing up, and because it's the backdrop for two things I've been unable to stop turning over.

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Two dogs from families who train with us live in the Tunbridge Wells area. The first belongs to an owner who switched to bottled water purely out of necessity, during the supply disruption — not as any kind of gut-health experiment.

What she noticed wasn't what she went looking for. Her dog's stools improved. Her behaviour started to settle.

The second is a dog with a long-standing history of gut trouble, whose owner switched him to bottled water on my dads advice. Same result.

Two cases. Not a clinical trial, not a peer-reviewed study — just two observations pointing the same direction, from the same corner of the map, at exactly the point that corner of the map was under formal regulatory scrutiny.

That doesn't prove anything on its own. But it's the kind of question a curious mind doesn't let go of easily, and I'm nothing if not curious.

My behaviourist (dad) has since had an undersink water filter fitted at his own house.

Not because he's certain of anything, but because good clinicians work by ruling things out, not ruling them in — and water is now a variable he can't confidently rule out anymore.

His own dog, one of my chaos crew, has a behavioural profile that's never been fully explained, and an unexplained profile means going through every environmental variable you can reasonably check. The filter, as he puts it, is just one more thing eliminated from the list. The question it's there to answer is whether water was ever part of the picture.

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Before I get into what water might actually be doing once it's inside the body, there's something worth clearing up first — something most people, including plenty of switched-on people, have believed their whole lives without it being true.

Most people in England assume their tap water has fluoride in it. It gets blamed for enough things that I suppose everyone's assumed it must be everywhere. It isn't.

Only around ten percent of England's population actually gets water with fluoride added, and those areas are concentrated in the Midlands and the North East. Kent and Surrey aren't fluoridated at all.

Which means the dogs at the centre of this — and the dogs sniffing at, or turning down, that bowl in Brasted — have never been drinking artificially fluoridated water in the first place.

I'm not raising this to let fluoride off the hook. I'm raising it to make a bigger point: most people have almost no real idea what's actually in the water their dog drinks every single day.

Not whether it's fluoridated.

Not which disinfectants are in it, or at what levels.

Not how those levels spike in the days after a supply disruption, when a network gets recharged and chlorine gets deliberately dialled up to stop anything nasty getting into the refilled pipes. The assumption that tap water is just... tap water — known, stable, harmless — doesn't hold up well once you actually look at the chemistry.

Fluoride does deserve its own separate word, on accumulation specifically, and this is where it gets genuinely relevant for dogs.

Fluoride sticks around in the body — about 99% of it ends up stored in calcified tissue, mainly bone and teeth, and it builds up over a lifetime.

The concern isn't that the fluoride levels found in English tap water are alarming by themselves — a 2025 systematic review in Nutrition Reviews found that at 2mg/L or below, the effect on gut microbiota was minimal.

The concern is the cumulative load. A person eats a varied diet over a varied lifetime, which dilutes chronic exposure to any one thing almost by accident.

A dog eating the same food from the same bag, drinking the same water, every single day of its life, doesn't get that dilution.

The Environmental Working Group found that combined fluoride from commercial dog food and water alone can get close to unsafe territory — before you've even added in what's coming from the water on top. This isn't settled science. It's barely even an asked question, which in my experience is usually the kind worth asking.

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Now, the actual mechanism.

Chlorine goes into drinking water to kill things, and it's good at its job.

What it isn't is selective — its job doesn't stop being its job the moment it comes out of the tap.

A study in the journal Science of the Total Environment, done in mice, found that chlorinated drinking water significantly reduced gut microbiota alpha-diversity compared to unchlorinated water.

The researchers noted that the shifts chlorination caused in the microbial community could be causal to gastrointestinal epithelial structure and function, not just correlated with it.

Another review flagged persistent low-level chlorine exposure as a potentially unrecognised risk factor for gut dysbiosis — that's the disruption of the microbial ecosystem living in the digestive tract, which the research now ties to a genuinely wide range of chronic conditions well beyond the gut itself.

A randomised controlled trial in infants found that chlorinated tap water increased the carriage of antibiotic-resistance gene pathways in gut microbiota — which tells you the microbiome's response to chlorine goes beyond simple species counts.

The direct research on dogs specifically is still thin on the ground.

But the biological pathway holds together, and it's backed up increasingly across other mammalian models.

Holding together isn't the same as proof. It is, though, a mechanism — and you need a mechanism before an observation stops being an anecdote and starts being a real question.

A disrupted gut microbiome doesn't stay politely contained in the gut. This is the part I think the behaviour profession really ought to be paying closer attention to.

Around 90% of the body's serotonin isn't made in the brain — it's made in the gut, by enterochromaffin cells that respond directly to whatever microbial environment surrounds them. The vagus nerve runs a constant two-way conversation between the gut and the brain, consistent and consequential enough that the gut has earned the nickname "the second brain," fairly. The HPA axis — the stress-response system that governs how a dog handles uncertainty, novelty, and challenge — is shaped in real part by what's going on in the gut microbiome. Dysbiosis doesn't stay put. It travels.

A 2025 critical review confirmed that early evidence now links canine gut microbiota to anxiety, aggression, and cognitive function.

Researchers have already identified specific bacterial signatures tied to anxiety-related behaviour in dogs, and distinct microbial profiles in dogs presenting with aggression.

A gut worn down by chronic exposure to antimicrobial compounds in drinking water isn't just a digestive footnote.

Neurologically speaking, it's an upstream variable sitting quietly behind the behaviour an owner eventually brings to a behaviourist as "the problem."

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Which brings me back to that paddling pool in Brasted.

We're choosing water that's been sitting in the sun and the air all morning, splashed about by every dog in the session.

We're turning down water drawn straight from the mains and poured, with the best of intentions, into a spotless bowl.

By the standards of human sight and human taste — the instruments you default to when deciding what's good — the bowl wins, easily. By the standards of 300 million scent receptors reading a dissolved chemical profile down to parts per trillion, the pool, chlorine mostly gone, sun-processed all morning, is a lot closer to what water is actually supposed to smell like.

You see water with your eyes. We smell it. Those aren't the same tool for this particular job, and one of them has been quietly getting the right answer this whole time while you've been putting it down to personality.

The supply area behind all this has been formally flagged by the regulator as a water quality concern — in some cases years before the public had any idea anything was wrong.

The dogs living on that supply have been drinking it every day of their lives.

The possibility that it's been leaving a mark — in the gut, in the microbiome, in whatever's shaping the behaviour you're seeing — isn't a comfortable thought. It is, though, a coherent one.

The behaviour profession has got much better over the last couple of decades at looking at what's happening inside a dog. Pain gets taken seriously now as a driver of behaviour. So does hormonal state. So does neurological function.

Water hasn't really entered that conversation yet, not in any meaningful way.

It might be the most invisible variable of the lot. It turns up every day. Everyone assumes it's fine. Nobody checks.

The dogs at that bowl were checking. We just weren't being listened to.

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I don't prescribe anything — never have, never will, and blanket advice was never really my style. But I will offer something that costs you almost nothing to try.

If your dog lives in the South East Water supply area — their regulatory record is public and linked below, so have a read yourself — water is now a variable worth actually looking at.

If your dog turns down water in unfamiliar places, or keeps going for the paddling pool over the freshly filled bowl, think about what that might be telling you.

If your dog has gut trouble nobody's explained, or a level of arousal that hasn't budged for anything else you've tried, water is a cheap, low-effort thing to test.

Try filtered.

Try bottled.

Let it stand first if you can manage it.

See what changes — in the gut, in how settled they are, in the general shape of the day.

Then take what you notice to your vet. Take it to your behaviourist. Add it to the whole picture of the dog in front of you.

I'm not asking you to decide the water's guilty. It's simpler than that, and it matters more.

When was the last time anyone thought to ask?

Nose to the ground, as ever — Percy

Sources

Drinking Water Inspectorate — South East Water Improvement Programmes (all current notices and enforcement orders, publicly searchable): https://www.dwi.gov.uk/water-companies/improvement-programmes/south-east-water-improvement-programmes

DWI Regulation 28(4) Notice — Pembury WTW Pesticides SEW-2024-00006 (completion date May 2031): https://www.dwi.gov.uk/water-companies/improvement-programmes/south-east-water-improvement-programmes/sew-2024-00006/

DWI — Section 18 Enforcement Order, Pembury Water Treatment Works SEW-2025-00042: https://www.dwi.gov.uk/water-companies/improvement-programmes/south-east-water-improvement-programmes

DWI Investigation — South East Water loss of supply, December 2025: https://www.dwi.gov.uk/4-december-2025-drinking-water-inspectorate-investigating-south-east-water-incident/

DWI Investigation — Kent and Sussex supply incidents, January 2026: https://www.dwi.gov.uk/13-january-2026-drinking-water-inspectorate-investigating-loss-of-supply-incidents-affecting-kent-and-sussex

DWI — Fluoridation of Drinking Water (England): https://www.dwi.gov.uk/consumers/learn-more-about-your-water/fluoridation-of-drinking-water/

Exposure to chlorinated drinking water alters the murine fecal microbiota — Science of the Total Environment, 2024

The Effects of Chlorinated Drinking Water on the Assembly of the Intestinal Microbiome — Challenges, 2019

Chlorinated Drinking Water Exposure Enriches Antimicrobial Resistance Pathways in the Infant Gut Microbiome: A Randomized Trial — medRxiv, 2024

Effect of Fluoride on Gut Microbiota: A Systematic Review — Nutrition Reviews, 2025

Gut-Brain Axis Impact on Canine Anxiety Disorders — PMC, 2024

The Relationship between Canine Behavioural Disorders and Gut Microbiome and Future Therapeutic Perspectives — Animals, 2024