The Weirdness of Water: A Field Guide

The Weirdness of Water: A Field Guide

Water is the most-studied liquid in the world. We drink it, swim in it, weather forecasts hinge on its phase changes, and roughly two-thirds of the human body is made of it. And yet, walk into any condensed matter physics department in 2026 and you will find people still arguing about what it is.

Most liquids are boring in the sense that they obey the same handful of generalizations: they contract when they freeze, their density rises monotonically as you cool them, their heat capacity is some unremarkable multiple of the universal gas constant. Water obeys almost none of those generalizations. Martin Chaplin’s catalogue at London South Bank University lists at least seventy distinct anomalies. Some are textbook; some are still actively researched; a couple have been the focus of papers, patents, and entire pseudoscientific movements. This essay is a tour of the ones I keep returning to — first the textbook surprises, then the active frontiers, then the macroscopic phenomena that have engineering consequences, then water in space, in biology, and finally the famous controversies that the field has had to spend energy debunking.

Throughout, the same protagonist is doing the work: a small, bent, polar molecule with two electron lone pairs and the ability to donate and accept hydrogen bonds in every direction. Almost every weird property of water can be traced back to the hydrogen-bond network, which is simultaneously strong (about 20 kJ/mol per bond, an order of magnitude above van der Waals) and labile (rearranging on picosecond timescales). The combination produces a substance that behaves like a solid and a liquid at the same time, and one for which “solid” itself takes more than twenty distinct forms.

Part 1 — The textbook anomalies

Density maximum at 4 °C, and ice that floats

The single most famous water anomaly is so familiar that we forget it is strange: liquid water reaches its maximum density at 3.984 °C, not at the freezing point. Cool fresh water from room temperature and it gets denser until you hit roughly four degrees Celsius, after which it gets lighter. Continue past zero and it freezes into ice Ih (ordinary hexagonal ice), which is lighter again — about 917 kg/m³ versus the liquid’s ~1000 kg/m³.

Almost no other common substance does this. Most liquids contract on freezing because the molecules pack tighter into a crystal than they do in disordered motion. Water’s hydrogen-bond geometry insists on a tetrahedral arrangement around every oxygen atom, and the resulting open lattice of ice Ih is roughly 9% less dense than the liquid it came from. The biological consequence is that lakes and oceans freeze from the top down. Ice forms on the surface, insulates the liquid below, and life carries on at the bottom. A planet whose ice sank would freeze solid from the floor up the first time it got cold enough — and probably would not host fish.

Highest specific heat capacity of any common liquid

Water absorbs and releases heat very reluctantly. Its specific heat capacity is about 4.184 J/g·K — roughly twice that of olive oil, an order of magnitude above most metals, and the highest of any familiar liquid that is not chemically exotic (liquid ammonia and liquid hydrogen do better). The reason, once again, is the hydrogen-bond network: heat that would normally go into translational and rotational degrees of freedom in a simple liquid instead goes into librational modes and into making and breaking bonds.

This is why oceans buffer climate, why coastal cities have milder winters and cooler summers than inland ones at the same latitude, and why “heat content” rather than “surface temperature” is the right way to think about global warming. The world ocean has stored over 90% of the excess energy trapped by anthropogenic greenhouse gases, and we measure the difference in tenths of a degree across many cubic kilometres.

Surface tension high enough to walk on

At 20 °C water has a surface tension of about 72.8 mN/m, more than three times that of typical organic solvents. The same hydrogen-bond cohesion that makes water reluctant to heat up makes its surface reluctant to be breached. Water striders walk on ponds because their weight per leg cannot overcome the cohesive force holding the surface together. The “pinned” contact angle on a hydrophobic surface, the meniscus you see in a glass capillary, and the upward transpiration of water through a redwood from roots to needles — over a hundred metres against gravity — all flow from the same property.

The redwood case is worth dwelling on. The transpiration column is held together by cohesion (water to water, via hydrogen bonding) and adhesion (water to cellulose-lined xylem walls). The column is under enormous tension — a redwood is, in effect, pulling a several-megapascal-suction straw a hundred metres tall — and only the strength of water’s hydrogen-bond network and the narrowness of the conduits keep cavitation from rupturing the column. When droughts get severe enough to push xylem into cavitation, trees die.

Dielectric constant high enough to be a universal solvent

Water’s static dielectric constant at room temperature is about 78.5, which is huge. It means an ionic compound dissolved in water sees its internal Coulomb attraction reduced by a factor of nearly eighty, which is why salts that would never come apart in vacuum dissociate freely in solution. Combine that with the molecule’s polarity, its ability to act as both proton donor and proton acceptor, and the small molecular size that lets it nestle into solvation shells, and you get the “universal solvent” of the chemistry textbook.

It is, however, not actually universal. Water is a very bad solvent for nonpolar substances — oils, fats, atmospheric gases other than CO₂, most hydrocarbons. The hydrophobic effect, which drives lipid membranes to self-assemble and protein hydrophobic cores to fold inward, is essentially the consequence of water’s preference for hydrogen-bonding with itself rather than wasting bonds on a nonpolar guest molecule. Life on Earth as we know it is structured around the boundary between things that water loves and things it does not.

Part 2 — The phase diagram is wild

Water has more solid phases than any other known pure substance. The IUPAC list as of 2026 stands at roughly twenty: ice Ih (ordinary hexagonal ice), ice Ic (a metastable cubic form found in upper-atmosphere ice clouds), and ices II through XIX in various crystalline forms, plus at least three distinct amorphous forms — low-density (LDA), high-density (HDA), and very-high-density (VHDA) amorphous ice. Different combinations of pressure and temperature stabilise different stacking arrangements of the tetrahedral hydrogen-bond network, sometimes proton-ordered (every hydrogen position fixed) and sometimes proton-disordered (hydrogen positions fluctuating subject to the ice rules).

Phase	Stability conditions	Notable features
Ih	0 °C to −200 °C, ambient pressure	Normal ice; hexagonal; what you see in your freezer
Ic	130–220 K, low pressure	Cubic; metastable; in mesospheric clouds
II	190–210 K, 0.3 GPa	Rhombohedral, fully ordered
III	≥ 0.3 GPa, ~250 K	Tetragonal
V, VI	Higher pressures, 200–270 K	Monoclinic / tetragonal
VII	3 GPa+, room temp	Hydrogen-disordered cubic; included in diamond inclusions
VIII	Cold version of VII	Hydrogen-ordered
IX	165–208 K, 0.2–0.4 GPa	Ordered form of III
X	~70 GPa	Proton-symmetric ice
XI	240 K, low pressure	Ferroelectric, very slow-forming, found in old Antarctic ice
XII	High-density metastable	From heating HDA
XIII–XV	Ordered counterparts of V, VI, XII
XVI	Empty clathrate framework	Least dense crystalline ice
XVII	Hydrogen-filled clathrate residue	Discovered ~2016
XVIII	~100–400 GPa, 3000–5000 K	Superionic ice
XIX	~2 GPa, 100 K	Ordered counterpart of VI; described ~2021
LDA, HDA, VHDA	Amorphous	Glassy ices; LDA may relate to LDL liquid water

That last entry hides the biggest open question in the field, which I’ll get to in the next section.

Superionic ice

Superionic ice (ice XVIII) is what happens when you compress water to between roughly 100 and 400 GPa and heat it to a few thousand kelvin simultaneously. Above the transition, the oxygen atoms remain locked in a body-centred cubic lattice, but the hydrogen nuclei (bare protons, essentially) de-localise and flow through the lattice like a liquid. The result is a solid by some definitions and a liquid by others — a crystal that conducts electricity through proton diffusion. Marius Millot and collaborators at the Omega laser facility at the University of Rochester’s Laboratory for Laser Energetics demonstrated superionic ice experimentally in 2019, using ramped laser shocks to compress thin layers of water to the relevant conditions for billionths of a second and using X-ray diffraction to confirm the body-centred cubic oxygen lattice. The result had been predicted by Pierfranco Demontis and colleagues in 1988, which is a respectable 31 years of waiting for experimental confirmation.

Superionic ice is not laboratory exotica. It is believed to comprise the bulk of the interiors of Uranus and Neptune. Both of those planets have strange, multipolar, off-centre magnetic fields that have never made sense in a conventional dynamo picture; an electrically-conducting superionic mantle, in contrast to a small dynamo region near the surface, is a leading candidate for the geometry that produces them. The chemistry of life happens in liquid water; the chemistry of ice-giant magnetism may happen in a solid one.

Hot ice in carbon nanotubes

In 2016, Michael Strano’s group at MIT reported that water confined inside carbon nanotubes a few angstroms in diameter could exist as a solid at room temperature and even above the normal boiling point. The phase transition temperature shifted by an enormous margin — over 100 °C in some cases — depending on the exact diameter of the tube. The mechanism is geometric: when the channel is narrow enough that the water column has only one or two molecules across, the bulk hydrogen-bond network collapses into a strictly one-dimensional motif, and that motif has its own thermodynamics in which the entropy gain on melting is much smaller than in bulk. The freezing transition becomes more favourable. Hot ice in a straw.

The same group and others have shown that water transport through carbon nanotubes is enormously faster than classical hydrodynamics predicts — several orders of magnitude — while the tubes simultaneously reject ions almost completely. This is one of the bases for graphene-oxide membrane desalination, an active engineering area that could in principle produce fresh water from seawater at a fraction of current energy costs.

The no-man’s-land

In the supercooled regime, between roughly −38 °C (where homogeneous nucleation of ice Ih becomes unavoidable in bulk water) and roughly −123 °C (where amorphous water reverts to a liquid on heating), water is nearly impossible to study because it crystallises faster than any ordinary experimental technique can probe. This is the “no-man’s-land,” and it is exactly where the most interesting open questions live. New techniques — ultrafast laser heating of HDA ice, microfluidic confinement that suppresses nucleation, X-ray free-electron laser pulses shorter than the crystallisation time — have begun to crack the region open over the last decade. What they appear to be finding is the subject of the next section.

Part 3 — Active research frontiers

Two-state model: LDL and HDL liquid water

The most provocative current idea is that liquid water is actually a fluctuating mixture of two distinct local structures: a low-density liquid (LDL), open and tetrahedral and ice-Ih-like, and a high-density liquid (HDL), more closely packed and disordered, related to the high-density amorphous ice. The two-state model is associated with H. Eugene Stanley and Pradeep Kumar and was put on rigorous footing by computer simulations of the ST2 and TIP4P water models throughout the 1990s and 2000s. It predicts that there exists a second critical point of water, deep in the no-man’s-land at perhaps 220 K and 100 MPa, where the LDL/HDL distinction becomes a continuous transition.

Until recently this was almost entirely a theoretical proposal. Within the last few years, experiments using femtosecond X-ray scattering at free-electron laser facilities — much of it from Anders Nilsson’s group at Stockholm and SLAC — have produced strong evidence that supercooled water genuinely does fluctuate between two distinct structural populations. Erik Lascaris’s PhD thesis, which the wiki citation links to, covers the simulation side of this in detail; it remains one of the more readable surveys.

If the picture holds up, then the explanation for all of water’s textbook anomalies (density max, expansion on freezing, anomalous compressibility) becomes much cleaner: the unique behaviour is the macroscopic shadow of that buried two-state structure.

Mpemba effect

Hot water sometimes freezes faster than cold water. The observation is ancient — Aristotle mentions it — but the modern revival is due to a Tanzanian schoolboy, Erasto Mpemba, who in 1963 noticed that his hotter ice-cream base froze faster than his cooler classmates’ and refused to be laughed out of the room about it. He and Denis Osborne published the effect in Physics Education in 1969.

The Mpemba effect has been replicated under controlled conditions and is also stubbornly difficult to pin down. Different experiments report it in different temperature ranges, with different container geometries, and different proposed mechanisms — evaporation, convection, dissolved-gas content, supercooling differences, frost-layer formation, even hydrogen-bond network “memory” of the warmer state. A 2017 paper by Lasanta and collaborators put forward a thermodynamic framework based on Markovian master equations that gives the effect a general (and counterintuitive) home: under some non-equilibrium conditions, a system can reach a lower temperature faster from a higher starting point. So the effect is plausibly real, plausibly explained, and still hard to demonstrate reproducibly. A 2020 study questioned whether the canonical “hot freezes faster” experiment ever passes a rigorous reproducibility test in bulk water; current consensus seems to be “in granular media yes, in water sometimes but fragilely.”

Ortho and para water

Like H₂ and a handful of other molecules with equivalent hydrogen nuclei, water comes in two nuclear-spin isomers. Ortho-water has the two proton spins aligned parallel (total nuclear spin I = 1); para-water has them antiparallel (I = 0). The two isomers cannot interconvert without flipping a nuclear spin, which is slow under normal conditions. They have different rotational ground states, slightly different infrared spectra, and — most strikingly — slightly different chemical reactivities. Pure para-water has been produced and trapped at cryogenic temperatures, and its reactivity in cold molecular collisions has been measured to be distinguishable from ortho-water’s. At room temperature the equilibrium ratio is 3:1 ortho-to-para, set by the spin-statistical weights, but that ratio drifts at lower temperatures and may matter in astrochemistry, where cold molecular clouds preserve non-equilibrium ortho/para ratios that record the history of the water-ice grains.

Pressure-induced metallization

Push water hard enough and it stops being an insulator. Theoretical predictions and shock-compression experiments suggest that at pressures on the order of 50 megabars (5,000 GPa), water becomes metallic — that is, its band gap closes and it conducts via delocalised electrons rather than via proton hopping. This is well beyond what diamond anvil cells reach, but laser-driven shocks and isentropic compression at facilities like LLE and the National Ignition Facility have started to probe the relevant regime. Metallic water (or its sibling, metallic hydrogen) is again of planetary interest: deeper into the Uranian and Neptunian interiors, conditions may favour electronic rather than ionic conduction, and the difference matters for understanding planetary magnetic dynamos.

Part 4 — Macroscopic phenomena

Cavitation and sonoluminescence

A water-handling engineer’s nightmare is cavitation: when local pressure in a pump or propeller drops below the vapour pressure, bubbles of vapour nucleate, are carried into a higher-pressure region, and collapse with enough violence to pit metal surfaces. The collapse is supersonic on its inner surface and concentrates an extraordinary amount of energy in a very small volume.

How much energy is in question. Under acoustic forcing — driving a single bubble to oscillate in a standing sound wave in a flask of degassed water — the collapse produces a flash of light. The phenomenon is called sonoluminescence and was discovered by Frenzel and Schultes in 1934 in the context of submarine sonar research. The temperatures inferred from the blackbody spectrum of the flash are tens of thousands of kelvin; some experiments have argued for hundreds of thousands. There are theoretical proposals — never confirmed and now generally regarded as implausible — that a sufficiently violent collapse could produce a brief fusion event. What is certain is that a centimetre-scale chunk of water sitting in a flask can be coaxed into producing a glowing point that, at its centre during the collapse, is hotter than the surface of the Sun for about a hundred picoseconds. Whatever the exact mechanism, it is a spectacular concentration of energy.

Solitons, rogue waves, and the canal at Hermiston

In August 1834, the Scottish engineer John Scott Russell was riding along the Union Canal near Edinburgh observing a barge being towed by a pair of horses. The barge suddenly stopped, but the bow wave it had been pushing kept going — as a single, smooth, round-topped wave of fixed shape, travelling at about eight miles an hour. Russell rode after it on horseback for nearly two miles, until the wave finally dissipated in the shallows. He named it the “wave of translation.”

The wave of translation was a solitary nonlinear wave: a soliton. Russell spent decades trying to convince the British mathematical establishment that what he had seen was real. He built tanks in his back garden and demonstrated solitons in them. His contemporaries, Airy among them, insisted that according to linear wave theory no such thing could exist. The Korteweg-de Vries equation, published in 1895, finally provided the mathematical framework that vindicated him. We now know that solitons appear in optical fibres, in plasmas, in Bose-Einstein condensates, and in oceans, and the field of integrable systems they spawned occupies a substantial corner of modern mathematical physics.

The closely related Peregrine soliton, predicted in 1983 and experimentally demonstrated in water tanks around 2010, is a candidate model for ocean rogue waves: rare, transient walls of water several times larger than the surrounding sea state that have sunk ships and which were dismissed as sailor tales until well-instrumented oil platforms started recording them in the 1990s. A rogue wave is, in this model, a nonlinear focusing of the surrounding wave field that concentrates energy from a much wider region into a single peak.

Armstrong’s water bridge

Put two beakers of pure water close together but not touching. Apply a high voltage — about 15 kilovolts — between them. Touch the water surfaces with the electrode tips to start, then slowly pull the beakers apart. A horizontal water bridge forms between the two beakers, suspended in air across the gap, sometimes maintaining itself across 25 mm or more. The phenomenon was first reported by Sir William George Armstrong in 1893 and has been periodically rediscovered since. Modern investigations (Fuchs and colleagues, 2007 onward) have measured the bridge’s birefringence, indicating partial alignment of water molecules along the field direction, and have inferred a slight density increase relative to bulk water. The proposed mechanism is some combination of dielectric polarisation, surface tension, and electro-hydrodynamic flow, but a fully quantitative theory has not, as far as I know, been settled. It remains the kind of demonstration that gets passed around physics departments on slow afternoons.

Why ice is slippery

You would think, after a few centuries of skating and curling, that we would know the answer to this. We did not, for most of those centuries. The traditional textbook explanation — that pressure from a skate blade melts the ice locally because of the negative slope of water’s solid-liquid phase boundary — is wrong by about an order of magnitude. A skater’s weight on a thin blade is not enough to depress the melting point by more than a fraction of a degree, far less than the slipperiness you actually observe at, say, −20 °C.

The right answer, settled mostly in the last decade, is that the surface of ice is intrinsically pre-melted. A few nanometres of “quasi-liquid” water exist on ice surfaces at temperatures well below the bulk freezing point — a consequence of the fact that the cost of an incomplete hydrogen-bond network is paid at any free surface and that water “pays” that cost by being locally disordered. The thickness of the quasi-liquid layer increases as temperature approaches 0 °C, which is why ice gets slipperier near the freezing point. The phenomenon has been imaged with atomic-force microscopy, characterised by sum-frequency generation spectroscopy, and simulated to death; physical reviews on the topic appeared throughout the late 2010s.

Clathrate hydrates

A clathrate hydrate is a crystalline lattice of water molecules whose cages enclose guest molecules — methane, CO₂, hydrogen, noble gases — that the water network grows around. The most famous variety is methane hydrate, vast quantities of which exist on continental shelves and in permafrost regions. A chunk of methane hydrate looks like dirty ice but will catch fire if you put a match to it: the methane is released as the cage destabilises, and burns. “Burning ice.”

The total amount of carbon locked up in marine methane hydrates is enormous — comparable to or exceeding all known conventional fossil-fuel reserves. This has been periodically eyed as a potential energy source (Japan and China have run extraction trials) and is correspondingly periodically eyed as a major climate hazard: a destabilising release of seafloor methane during a warming event is a candidate trigger for the Paleocene-Eocene Thermal Maximum 56 million years ago, and the analogous event under a different climate forcing today is the kind of thing climate scientists lose sleep over.

Empty clathrate frameworks — ice XVI in the IUPAC list — are themselves the least dense known crystalline ice and can in principle be filled with arbitrary guests. There is real research on hydrogen-storage clathrates as a transportation fuel medium.

Plasma-activated water

Strike an electrical discharge in or just above water and you get water populated by short-lived reactive species — hydroxyl radicals, atomic oxygen, hydrogen peroxide, nitric oxide derivatives, hydrogen radicals. This “plasma-activated water” (PAW) is a real area of agricultural and medical chemistry: the radicals are strong oxidants and have been used for surface sterilisation, wastewater treatment, and crop disease control. Paul Leenders, mentioned on the wiki, has run a Dutch consortium on agricultural PAW; the IEEE Xplore citation on the page covers the electrochemistry. As a substitute for synthetic pesticides, PAW has genuine promise. As a snake-oil sold by “vitalised water” merchants, it has also been periodically misused. The chemistry is sound; the marketing varies.

Part 5 — Cosmic and planetary water

Subsurface oceans

The biggest astronomical story about water in the last twenty years is that liquid water is far less rare than we thought. The Galileo mission returned magnetometer signatures from Europa, Ganymede, and Callisto that are most easily explained by salty conducting layers under their icy crusts. Cassini’s flybys of Enceladus, the small Saturnian moon, directly sampled water-ice plumes erupting from the south polar region, finding organic molecules, hydrogen, and silica grains consistent with ongoing hydrothermal activity at the rocky core. Hubble and JWST have observed plume-like behaviour on Europa. The Juno mission has hinted at similar things at Io’s nearest cousins. Subsurface oceans appear to be common on the icy moons of Jupiter and Saturn, plausibly on Triton, and arguably on Pluto.

This matters for astrobiology because liquid water plus chemistry plus energy is the recipe we have for the only biosphere we know about. None of these moons gets significant sunlight, but tidal heating from the parent planet, plus chemistry at hydrothermal vents, can plausibly drive a biosphere chemically. Europa Clipper, which arrived in Jupiter orbit in the early 2030s, is specifically designed to test the habitability of Europa’s ocean.

Where did Earth’s water come from?

Deuterium-to-hydrogen ratios are a fingerprint. Different reservoirs in the early solar system formed with different D/H ratios depending on their temperature and chemistry, and water that condensed in those reservoirs retains the ratio it had when it froze out. The D/H ratio of Earth’s ocean water (the so-called Vienna Standard Mean Ocean Water, about 156 ppm) is a clue to where it came from.

For decades, the leading hypothesis was that Earth’s oceans came mostly from cometary impacts during the late heavy bombardment. The Rosetta mission’s measurements of D/H in the coma of comet 67P/Churyumov-Gerasimenko, published 2014, threw a wrench in this story: 67P’s water was three times the Earth-ocean ratio, far higher than expected and inconsistent with comets having delivered the bulk of Earth’s water. The current preferred picture is that most of Earth’s water came from carbonaceous chondrite-like asteroids whose D/H ratios are much closer to ocean water, with comets contributing a minority. That isn’t settled — Hartley 2 had an Earth-like D/H, individual comets vary — but it is the cleanest explanation we have at the moment.

Mars and the water that nearly was

Mars had liquid surface water for at least a billion years in its early history. The geological record is unambiguous: ancient river deltas, shorelines, evaporite deposits, hydrated minerals. The atmosphere was thicker and warmer, the magnetic field was active enough to shield the surface, and water was stable as a liquid in places. Then the core dynamo shut down, the solar wind stripped most of the atmosphere over hundreds of millions of years, and the planet froze.

What is left today is mostly ice, much of it polar, much of it subsurface. Curiosity and Perseverance keep finding evidence of recurrent slope lineae and brine flows; perchlorate salts depress the local freezing point enough that transient liquid water on the modern surface is plausible in some seasons. Mars Reconnaissance Orbiter’s SHARAD radar has located a candidate subglacial liquid lake beneath the south polar cap, though that result has been contested and may turn out to be hydrated clay rather than liquid. The story of Mars is, in a sense, a counterfactual for Earth: what happens when a rocky planet loses its magnetic field and slowly loses its atmosphere. Water is the marker we use to read that history.

Part 6 — Biological water

The water inside a living cell does not behave like the water in a beaker. Within a few angstroms of any protein surface, water molecules are oriented, their hydrogen-bond network biased by the local chemistry of the protein, their rotational reorientation times stretched from a couple of picoseconds in bulk to tens of picoseconds. Two-dimensional infrared spectroscopy and ultrafast pump-probe techniques over the last two decades have made this “biological water” or “hydration water” something that can actually be measured. It is not the mystical “structured water” of pseudoscience; it is a measurable, computable layer that decays with distance from the surface over a few angstroms. But it is also not the same as bulk water, and a lot of biophysics depends on the difference. Protein folding, ligand binding, allostery, even the diffusion of small molecules across membranes are all modulated by the local properties of the hydration shell.

Then there are organisms that engineer water at the macroscopic level. Antarctic notothenioid fish, snow fleas, several insects, and a number of overwintering plants secrete antifreeze proteins — molecules that bind to nascent ice crystal surfaces and pin further growth, depressing the freezing point of the organism’s body fluids by several degrees without affecting the equilibrium melting point. The bound proteins distort the ice surface such that further water addition is thermodynamically unfavourable. This is “thermal hysteresis,” and it lets the fish in question swim around in seawater at −2 °C without turning into a popsicle. The same trick is now being applied in food science to keep ice cream smooth.

A small detour into the hydrophobic effect, which I mentioned earlier: when an oil droplet sits in water, the water molecules at the interface must arrange themselves to satisfy as many hydrogen bonds as possible despite the oil being unable to participate. This forces them into a more ordered “iceberg” arrangement that costs entropy. The system can recover that entropy by pushing oil droplets together so the total interfacial area shrinks — and that is the driving force of the hydrophobic effect. Lipid bilayer self-assembly, micelle formation, and the burial of nonpolar amino acid side chains in protein cores all run on the entropy of water surrounding hydrophobic things, not on any direct attraction between hydrophobic objects themselves. Life is, in a real sense, a phenomenon that emerges from water’s preferences.

Part 7 — Fringe and pseudoscience

Water’s genuinely strange behaviour has, predictably, attracted a parade of claims that are not strange in the right way. A few are worth naming explicitly, partly because anyone reading about real water anomalies will eventually run into them, and partly because the debunking process itself is interesting.

Polywater

In 1962 the Soviet chemist Nikolai Fedyakin reported that water condensed in narrow quartz capillaries had unusual properties: higher density, higher viscosity, a different freezing point. Boris Derjaguin took up the work, named the substance “anomalous water” (later “polywater”), and proposed it was a polymerised form of H₂O. The claim spread to the West in the late 1960s and produced hundreds of papers, including breathless speculation that if polywater escaped the laboratory it might seed normal water into the polymerised form and end life on Earth — an Ice-nine scenario in real time.

The whole thing collapsed by about 1973 when better analytical techniques showed that the “polywater” samples were heavily contaminated with silica leached from the quartz, plus various organic impurities. Polywater was an artifact. The episode is now standard reading in philosophy-of-science courses as a worked example of confirmation bias, the social dynamics of an emerging research community, and how fragile-but-cheap measurements can hold a whole field hostage. Felix Franks’s 1981 book Polywater is the canonical history.

Water memory

In 1988, the immunologist Jacques Benveniste published a paper in Nature claiming that human basophil cells responded to extremely dilute solutions of anti-IgE antibody — so dilute that, by elementary stoichiometry, not a single antibody molecule should remain. The implication was that water somehow retained a “memory” of the antibody. The paper was published with an editorial note from Nature that it would be independently investigated, and a delegation including James Randi visited Benveniste’s lab. The follow-up investigation found systematic problems with the blinding protocol and could not replicate the result.

“Water memory” became, and remains, the central scientific argument underpinning homeopathy. Independent replications continue to fail. The field has periodically been revisited — most notably by Luc Montagnier in the 2000s, with similarly non-replicable results — and remains outside the mainstream. The textbook objection is that hydrogen bonds in liquid water rearrange on the order of picoseconds: any hypothetical “structure” imprinted on bulk water by a solute would dissolve essentially instantaneously into thermal motion. There is no known mechanism by which liquid water could retain a chemical memory on biologically-relevant timescales.

EZ water and the “fourth phase”

Gerald Pollack’s group at the University of Washington has reported that water adjacent to certain hydrophilic surfaces (Nafion membranes, for example) forms a layer hundreds of micrometres thick that excludes dyes and other solutes — the “exclusion zone” or EZ water. Pollack interprets this as a “fourth phase” of water, with a stoichiometry of H₃O₂ and distinct optical, electrical, and chemical properties.

The exclusion-zone observation itself is real and reproducible: there is indeed a region near hydrophilic surfaces in which solutes are depleted and the water has slightly different properties from bulk. The mainstream explanation is electrokinetic — surface charges on the membrane drive ion gradients and a long-range diffusive depletion zone — and does not require any new phase of water. Pollack’s broader claims (that EZ water charges itself by absorbing infrared radiation, that it explains how blood circulates without a heart pump, that drinking it has health benefits) have not been independently replicated and have moved progressively away from peer-reviewed venues. The 2013 popular book The Fourth Phase of Water is widely cited by alternative-health marketers selling “structured water” devices.

Hexagonal water, vitalised water, structured water

A large and lucrative industry sells filters, vortexers, and magnets that claim to produce “hexagonal,” “structured,” or “energised” water with health benefits. None of these claims has survived independent testing. The molecular structure of liquid water at room temperature is a dynamic mixture of locally-tetrahedral arrangements that interchange on picosecond timescales; no plumbing device can impose a persistent “hexagonal” structure on it that would survive being drunk. The marketing trades on the fact that ice Ih really is hexagonal, that water really has unusual properties, and that the underlying physics is sufficiently complicated that a vague rhetoric of “structure” sounds plausible to a non-specialist.

The genuine weirdness of water is the perfect breeding ground for this sort of thing. The defence is, as always, to insist on the same standards of replication, blinding, and mechanism for water claims as for any other physical claim. The actual physics is strange enough.

Part 8 — Historical asides

Brownian motion

In 1827, the Scottish botanist Robert Brown was looking through a microscope at pollen grains suspended in water, trying to figure out the mechanics of plant fertilisation. He noticed that the tiny pollen grains were perpetually jiggling. He showed the same thing happened with inert dust and with finely-ground inorganic matter; it was not a biological phenomenon. He had no theory for what the jiggling was.

It took until 1905 for Einstein, in one of his annus mirabilis papers, to derive the diffusive motion of the pollen grains as the consequence of repeated random kicks from the surrounding water molecules. Jean Perrin’s experimental verification in 1908 nailed down Avogadro’s number and Boltzmann’s constant simultaneously, won Perrin a Nobel in 1926, and — among many other things — silenced the remaining sceptics of the atomic hypothesis. The first observed evidence that matter is made of atoms came from a botanist looking at pollen in a drop of water.

Heavy water and the Norwegian sabotage

Deuterium oxide, D₂O, is chemically almost identical to ordinary water but has a higher boiling point, a slightly different freezing point, and a different refractive index. It also slows neutrons in a nuclear reactor better than ordinary water does. During World War II, the Vemork hydroelectric plant in Norway, operated by Norsk Hydro, was the only large industrial producer of heavy water in Europe. The German nuclear weapons programme depended on Vemork’s output.

A series of British and Norwegian commando raids over 1942–1943 culminated in Operation Gunnerside in February 1943, in which a small team of Norwegian SOE-trained operatives skied across the Hardangervidda plateau in winter conditions, descended a ravine that the German garrison had judged unscaleable, and destroyed the heavy water cell room with explosive charges. A follow-up sabotage in February 1944 sank the ferry Hydro carrying the remaining heavy water inventory to Germany. The German nuclear programme was set back substantially. The 1965 film The Heroes of Telemark covers the story, somewhat romanticised. It remains, depending on how you count, one of the most consequential commando operations of the war.

Closing

After all of that, what is left?

A lot. We still do not have a fully accepted theory of the supercooled regime. We do not know whether the proposed second critical point of water genuinely exists, or whether the two-state picture survives more stringent tests, or how to reconcile the diverse experimental probes of the LDL/HDL distinction with each other. We do not have a clean microscopic theory of sonoluminescence. We do not have a satisfactory quantitative account of Armstrong’s water bridge. We are still arguing about which planetary bodies harbour subsurface oceans liquid enough to host chemistry. We are still, after decades, finding new crystalline ice phases.

Water is the textbook example of how a chemically simple molecule, given enough degrees of freedom in its hydrogen-bond network, can produce phenomena that span centuries of physics. It is also the textbook example of how genuine scientific weirdness is a magnet for less-disciplined imitations, and of how a research community has to keep adjudicating the boundary between the two. Martin Chaplin’s catalogue of seventy anomalies is a fine place to lose an afternoon; Lascaris’s thesis is a fine place to lose a week. The whole subject has the rare quality, in 2026, of being a thing every human encounters every day and that science has not finished explaining.

References and further reading

• Chaplin, M. Water Structure and Science. London South Bank University. https://water.lsbu.ac.uk/water/ — the canonical online catalogue, including the seventy-anomalies list.
• Lascaris, E. Liquid-Liquid Phase Transitions and Water-Like Anomalies in Liquids. PhD thesis, Boston University, 2014. https://physics.bu.edu/~erikl/research/Lascaris_PhD-defense_09july2014.pdf
• Millot, M. et al. “Nanosecond X-ray diffraction of shock-compressed superionic water ice.” Nature 569, 2019. Phys.org coverage: https://phys.org/news/2019-05-giant-lasers-crystallize-shockwaves-revealing.html
• Pollack, G. The Fourth Phase of Water (2013). TEDxGuelphU lecture: https://youtu.be/i-T7tCMUDXU. See independent review for the controversy.
• Stanley, H. E.; Kumar, P.; et al. Many papers on the two-state hypothesis through the 1990s and 2000s; the Stockholm/SLAC group (Nilsson, Pettersson) provided the modern experimental backbone.
• Nilsson, A. SLAC public lecture, “Water: the Strangest Liquid” (24 February 2009). https://youtu.be/7hGqlEpvODw
• Barbosa, M. “The weirdness of water could be the answer.” TEDxCERN. https://www.youtube.com/watch?v=-OLFwkfPxCg
• Lasanta, A.; Vega Reyes, F.; Prados, A.; Santos, A. “When the hotter cools more quickly: Mpemba effect in granular fluids.” Phys. Rev. Lett. 119, 2017.
• Strano, M. et al. “Anomalous freezing of water confined in carbon nanotubes.” 2016. MIT news release: https://news.mit.edu/2016/carbon-nanotubes-water-solid-boiling-1128
• Salzmann, C. G.; Rosu-Finsen, A. et al. on ice XIX and related newly-described crystalline phases, ~2021.
• Russell, J. S. Report on Waves (1844), British Association for the Advancement of Science. The Union Canal observation is in §1.
• Kirby, B.; et al. on the rogue-wave / Peregrine-soliton analogy in water tanks. https://www.nature.com/articles/nphys1740
• Franks, F. Polywater. MIT Press, 1981.
• Maddox, J.; Randi, J.; Stewart, W. “‘High-dilution’ experiments a delusion.” Nature 334, 1988 — the Benveniste investigation.
• Mpemba, E. B.; Osborne, D. G. “Cool?” Physics Education 4, 1969.
• The Heroes of Telemark (1965) — dramatised but readable take on Operation Gunnerside.

Comments, corrections, additional anomalies welcome.