Water is the substance we’re most made of, and the one we tend to think least about.
Roughly 60% of your body is water — closer to 75% of your brain, and around 80% of your lungs. Every enzyme reaction, every cell membrane, every hormone signal happens in it. When patients come to me with fatigue, headaches, poor concentration or stubborn skin, the first question I ask myself isn’t which supplement to reach for — it’s whether they’re drinking enough, and drinking well.
The basics: how much, and why
Adult guidelines suggest around 1.5–2 litres a day of fluid overall — a figure that includes water from food (particularly fresh fruit and vegetables), not only what you drink. Quantity, in any case, isn’t the whole story. Water isn’t a passive solvent that fills you up — it’s the medium of every reaction that keeps you alive. Cells that are chronically slightly dehydrated don’t detoxify well, don’t produce energy efficiently, and don’t clear waste from the brain properly during sleep. Mild dehydration is one of the most common — and most missed — drivers of afternoon fatigue and mental fog.
When more water isn’t the answer
It is also possible to drink too much water. Hyponatraemia — a dangerous drop in blood sodium from over-drinking — is well-documented, particularly in endurance athletes and health-conscious over-drinkers who force fluids all day. And if you find yourself constantly thirsty, unable to satisfy that thirst however much you drink, that in itself is worth investigating. Persistent excessive thirst can point to an endocrine or hormonal imbalance — diabetes (both types), diabetes insipidus, thyroid or adrenal issues, or raised blood calcium. That is a conversation with your GP, not simply more water.
Not all water is the same
UK tap water is safe by regulatory standards, but “safe” isn’t the same as “clean.” Chlorine and chloramine (added as disinfectants), fluoride (in some areas), trace pharmaceuticals, microplastics, and heavy metals from older pipework are all present at low levels. None will kill you, but the cumulative load matters — particularly for anyone whose detoxification pathways are already under pressure through mould illness, chronic infection, hormonal disruption or autoimmunity.
There’s a second concern beyond the chemistry. Chlorine and chloramine kill bacteria — that’s why they’re added. But they don’t discriminate, and drinking chlorinated water day after day is a low-dose antimicrobial delivered straight to the gut microbiome you spend the rest of your effort protecting. The research on fluoride’s impact on the oral and gut microbiome is heading in the same direction. For anyone rebuilding gut health after antibiotics, food poisoning or long-term use of PPIs, taking chlorine and fluoride out of drinking water makes intuitive sense.
Bottled water — the plastic problem
Bottled water is often the default alternative to tap. It’s rarely a good one. A 2024 study by researchers at Columbia University, published in PNAS, used new imaging techniques to find that bottled water contains an average of around 240,000 plastic particles per litre — 90% of them nanoplastics, small enough to cross cell membranes. Alongside the plastic itself, BPA, phthalates and other endocrine-disrupting compounds leach into water from plastic bottles, particularly when the bottle has been warmed in a car, on a shelf, or during transport.
If you want the convenience of a portable bottle, glass or high-grade stainless steel is a much better choice — refilled from a filter, not from another plastic bottle.
The fourth phase: why water may be more than we thought
Beyond solid, liquid and gas, Dr Gerald Pollack — a bioengineer at the University of Washington — has spent decades documenting a fourth phase of water: a structured, gel-like state that forms at the surface of biological tissues. In The Fourth Phase of Water (2013) he shows that this “exclusion zone” water behaves differently from bulk water — it holds a negative charge, excludes solutes, and appears to be the state in which most cellular water actually exists. The evidence is mounting: the water inside our cells is not the same substance that comes out of the tap.
This is emerging science; it sits at the edge of mainstream physiology. It points to a genuinely interesting idea — that how our body organises water may matter as much as how much of it we drink.
Water as it’s found in nature
Pollack’s work has an interesting practical implication. Water inside living things — the flesh of a ripe apple, the juice of a coconut, fresh spring water that hasn’t been boiled or pumped through miles of pipework — is already in this gel-like, structured state. Advocates of this thinking argue that eating your water, through fresh vegetables, fruit and unprocessed plant food, hydrates your cells more efficiently than drinking large volumes of tap water — and that a diet rich in high-water-content plants may reduce how much you actually need to drink to feel well.
The clinical evidence is preliminary and I wouldn’t build a treatment plan on it. But as a principle, it’s sound: whole plants, real food, spring water where you can get it — and less anxiety about hitting a specific litre count.
Structured water at home
The idea of “structuring” drinking water has moved from the fringe of biophysics into the wellness market. Devices such as Analemma claim to alter the molecular arrangement of tap water via a mineral resonance chamber. The clinical evidence is preliminary. For patients who want to explore this territory, it’s worth knowing about, and the underlying science (Pollack, and now others) is legitimate research rather than marketing.
Practically: filtering your tap water
For most patients the highest-impact change isn’t a structuring device — it’s a good filter. What I’ve seen work in London homes:
- Ceramic gravity filters — British Berkefeld (the original UK-made design, from Fairey Ceramics in Staffordshire) and Berkey (well-known, though not currently UK/EU-certified). Countertop, simple, no plumbing.
- Under-sink and countertop ceramics — Doulton, the British ceramic standard.
- Reverse osmosis — Osmio, UK specialists; removes the widest range of contaminants but strips minerals too, so remineralisation matters.
- Whole-house systems — Culligan if you want to filter every tap and shower — skin absorbs chlorine too.
Choose to your water supply, budget and household size. None of this is essential; all of it helps.
What I ask my patients to do
Three simple habits do most of the work:
- Drink a large glass of good-quality filtered water first thing, before coffee or breakfast. Overnight is the longest fast your body does, and you wake mildly dehydrated.
- Aim for around 1.5 litres across the day, sipped rather than gulped — less if your diet is already rich in fresh fruit and vegetables, more if you’re very active or in hot weather.
- Filter what comes out of the tap. Not perfect, not fancy — just clean.
Water is the cheapest, most fundamental medicine you have. Drink it well.
