Fourth Phase of Water in Your Body: What Has Been Measured

The fourth phase of water is a term from interface research, and for the water in your body there are solid measurements behind it, from the laboratory and from living cells. Next to water-loving surfaces in the lab, a zone typically several hundred micrometers wide forms, and dissolved particles are pushed out of it. That is about 5 times the width of a human hair, which measures around 70 micrometers. In living cells, about 85% of the water behaves like ordinary water. The remaining 15% sits directly on the surfaces of biomolecules and moves about 15 times more slowly there, with a rotation time of 27 picoseconds. Up to 60% of an adult body is water, and the most intriguing share is the part that lies on such surfaces. Whether the zone is a phase of its own or a transport effect at the interface has been debated for more than 20 years. So far it has been studied on lab surfaces and in bacterial cells.

What is the fourth phase of water?

Gerald Pollack, professor of bioengineering at the University of Washington, uses the term “fourth phase” for an ordered, gel-like layer of water directly next to water-loving surfaces. The name places it alongside the three familiar states of matter: solid, liquid, and vapor.

The effect itself has a plainer name: the exclusion zone, or EZ for short. Researchers add tiny plastic microspheres or a dye to water and watch them disappear from a region close to the surface. What remains is a visibly clear layer.

Several groups have repeated this observation independently of one another. The open question is how to interpret it, and in particular whether a distinct phase is really behind it.

How large is such a zone? Several hundred micrometers. A human hair is around 70 micrometers in diameter, so the zone is several times as thick as a hair. A hydration shell made of a few molecular layers ends in the nanometer range, and the zone reaches roughly 100,000 times farther. That gap in scale is exactly why the observation drew so much attention.

How much of your body water sits at a surface?

Body water is all the water in an organism, spread across the cells, the space between them, and the blood plasma. The US Geological Survey puts the water content of adults at up to 60%. For the lungs the figure is about 83%, for the skin 64%, and even bones still hold 31%.

How much of that water sits at a surface can be estimated. According to a systematic count, an adult body consists of around 3.72 × 10¹³ cells, or roughly 37 trillion. Each has an outer membrane and, inside, a densely packed framework of proteins and membranes. The smaller a container, the more surface it has relative to its contents. In a typical cell 20 micrometers across, simple geometry puts every water molecule no more than 10 micrometers from the nearest membrane.

How much water counts as surface water then depends on how far a surface reaches into the water:

Assumed reach of the surface	What it means for cell water
1 nanometer (classic hydration shell)	a small percentage of cell water
100 nanometers	a clear but limited share
100 micrometers (exclusion-zone scale)	on paper, all of the cell water

The reach decides whether ordered interfacial water in the body would be a marginal phenomenon or the normal case. Geometry cannot settle that, only measurement can. Researchers have done exactly that in living cells.

What was measured at the exclusion zone?

An exclusion zone is a region next to a water-loving surface where dissolved and suspended particles are far rarer than in the rest of the water. The central paper on it appeared in 2006 in Advances in Colloid and Interface Science. Zheng, Chin, Khijniak, Khijniak, and Pollack describe their finding in these words.

“We report here that colloidal and molecular solutes suspended in aqueous solution are profoundly and extensively excluded from the vicinity of various hydrophilic surfaces. The width of the solute-free zone is typically several hundred microns.”

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Zheng et al.: Surfaces and interfacial water: Evidence that hydrophilic surfaces have long-range impact. Advances in Colloid and Interface Science 127(1), pages 19–27 (2006), DOI 10.1016/j.cis.2006.07.002

The group tested the effect on many surfaces, including artificial and natural hydrogels, biological tissue, and ion-exchange beads. They used several methods as well: microscopy, electrical potential, UV-Vis spectroscopy, infrared imaging, and NMR imaging.

A later NMR study from the same lab found two separate water signals around Nafion and gel beads. Both showed shorter relaxation times and smaller diffusion coefficients than pure water (Yoo, Paranji, Pollack, Journal of Physical Chemistry Letters 2, pages 532–536, 2011, DOI 10.1021/jz200057g).

The exclusion is large, and very different methods detect it. All of these experiments ran on artificial or isolated surfaces in the lab.

Separate phase or diffusiophoresis: how do researchers explain the zone?

In physics, a phase is a state of matter with uniform properties throughout, set apart from its surroundings by an interface. Ice, liquid water, and steam are the familiar examples. Pollack sees the exclusion zone as one more state of this kind.

In a 2020 review, Daniel Elton, Peter Spencer, James Riches, and Elizabeth Williams laid the existing explanations side by side and weighed them. Pollack and others, they note, hold that water in the EZ has a different structure from bulk water, and that this structure accounts for the zone. On the alternative, the authors write as follows.

“We present several alternative explanations for EZs and argue that Schurr's theory based on diffusiophoresis presents a compelling alternative explanation for the core EZ phenomenon.”

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Elton, Spencer, Riches, Williams: Exclusion Zone Phenomena in Water: A Critical Review of Experimental Findings and Theories. International Journal of Molecular Sciences 21(14), article 5041 (2020), DOI 10.3390/ijms21145041

Diffusiophoresis means that particles migrate along a concentration gradient of dissolved substances. A Nafion surface releases ions, which sets up such a gradient, and the beads get pushed away. The water in between would not have to change its structure at all. The theory also predicts how the zone grows over time, and that prediction has been confirmed.

Both explanations fit the same observation. The review names several confounding factors that make experiments on exclusion zones tricky, such as charged surface groups, dissolved solutes, and adsorbed nanobubbles. The question is still open, and research on it continues.

What was measured in living cells?

Cell water is the water inside a living cell, as distinct from the water between cells and in the blood. When people talk about ordered body water, this is the water they really mean, and there is a direct measurement of it in living organisms.

Erik Persson and Bertil Halle grew bacteria in heavy water. They then tracked the relaxation rate of the deuterium nuclei across a wide range of magnetic fields, from 0.2 millitesla to 12 tesla. Their result appeared in PNAS in 2008.

“Contradicting the view that a substantial fraction of cell water is strongly perturbed, we find that approximately 85% of cell water in Escherichia coli and in the extreme halophile Haloarcula marismortui has bulk-like dynamics. The remaining approximately 15% of cell water interacts directly with biomolecular surfaces and is motionally retarded by a factor 15 +/- 3 on average, corresponding to a rotational correlation time of 27 ps.”

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Persson, Halle: Cell water dynamics on multiple time scales. PNAS 105(17), pages 6266–6271 (2008), DOI 10.1073/pnas.0709585105

For body water, these are the values that matter most:

• 85% of cell water moves like ordinary water.
• 15% lies on biomolecular surfaces and is slowed by a factor of 15 ± 3, which corresponds to a rotation time of 27 picoseconds. A picosecond is one trillionth of a second.
• 0.1% sits in deep binding pockets and exchanges only on the microsecond scale.

For living cells, measured in bacteria, the original question now has an answer. Part of the cell water really does move differently from the rest. It is the smaller part, and it turns somewhat more sluggishly. How sluggishly? Its rotation time is around 27 picoseconds. Persson and Halle designed their measurement to settle an older dispute about the properties of cell water, which they themselves call a long-standing controversy.

The next step: measuring ordered water in humans

Research has now traveled from the surface in a test tube to the living cell. The first stage is exclusion at a surface, several hundred micrometers wide and repeated on many materials. The second is the slowed minority of cell water in bacteria, 15% at a factor of 15. The exciting next step is to learn how ordered the body water of a human being is, and whether and how it can be influenced from outside.

To study that in living people, research needs three things:

1. A measurement method for the living human. The deuterium (²H) relaxation method works with cells grown in heavy water.
2. A reference value. It states how ordered the body water of a healthy person is.
3. Clinical studies with this endpoint. They build on the measurement method and the reference value.

Why Qi Blanco follows research on water and order

Qi Blanco is a brand of jewelry and everyday objects, and the subject that occupies us is water and order. For that reason we follow the research closely, from the exclusion zone at a gel surface to the water inside a living cell. We keep track of what has been measured and what is still open.

Readers who want to go deeper into the physics will find more in our articles Does Water Have Memory? What Physics Has Actually Measured and Cellular Hydration: What Water Really Does Inside Your Cells. How the subject has made its way into everyday life is the story of Is Structured Water Real? What Measurements Show. The research we cite on our own subjects is collected on our studies page.

Frequently asked questions about body water and the fourth phase

Is the fourth phase of water scientifically recognized?

Several groups have shown the zone itself independently: next to water-loving surfaces, a particle-free region several hundred micrometers wide forms. How to explain it is still under discussion. Gerald Pollack sees a phase of its own with a different structure. The 2020 review by Elton and colleagues finds a transport process along an ion gradient more convincing.

How much of the water in the body is ordered interfacial water?

For living bacterial cells there is a figure. About 15% of the cell water lies directly on biomolecular surfaces and moves around 15 times more slowly there. The other 85% behaves like ordinary water (Persson and Halle, 2008). A comparable measurement in human cells is still to come.

Can the water in a human body be structured?

So far, the order of water has been studied on surfaces in the lab and in bacterial cells. For the living human, research first needs a method that measures how ordered the water is, and a target value. With both in hand, a change could be detected as well.

What is the difference between a hydration shell and an exclusion zone?

A hydration shell is the layer of a few water molecules that directly surrounds a dissolved particle, and it reaches only a few nanometers. An exclusion zone extends roughly 100,000 times farther. The whole discussion turns on exactly that difference in size.

Key takeaways on ordered body water

• Up to 60% of an adult body is water, and the most intriguing share is the part that lies on a surface.
• Next to water-loving surfaces, a particle-free zone typically several hundred micrometers wide has been measured in the lab (Zheng et al., 2006).
• Whether this zone is a phase of its own is under discussion; a 2020 review finds diffusiophoresis the more convincing explanation.
• In living bacterial cells, about 85% of cell water behaves like ordinary water, and 15% is slowed at surfaces by a factor of 15 (Persson and Halle, 2008).
• That slowing plays out on a scale of 27 picoseconds, which is to say trillionths of a second.
• The next step for research on humans is a measurement method for the living body, a reference value, and clinical studies built on both.

Sources and further reading

• Zheng, J.-M.; Chin, W.-C.; Khijniak, E.; Khijniak, E.; Pollack, G. H.: Surfaces and interfacial water: Evidence that hydrophilic surfaces have long-range impact. Advances in Colloid and Interface Science 127(1), 19–27 (2006). https://doi.org/10.1016/j.cis.2006.07.002
• Persson, E.; Halle, B.: Cell water dynamics on multiple time scales. Proceedings of the National Academy of Sciences 105(17), 6266–6271 (2008). https://doi.org/10.1073/pnas.0709585105; PubMed record: https://pubmed.ncbi.nlm.nih.gov/18436650/
• Elton, D. C.; Spencer, P. D.; Riches, J. D.; Williams, E. D.: Exclusion Zone Phenomena in Water: A Critical Review of Experimental Findings and Theories. International Journal of Molecular Sciences 21(14), 5041 (2020). https://doi.org/10.3390/ijms21145041; free preprint: https://arxiv.org/abs/1909.06822
• Yoo, H.; Paranji, R.; Pollack, G. H.: Impact of Hydrophilic Surfaces on Interfacial Water Dynamics Probed with NMR Spectroscopy. Journal of Physical Chemistry Letters 2, 532–536 (2011). https://doi.org/10.1021/jz200057g; PubMed record: https://pubmed.ncbi.nlm.nih.gov/22003430/
• Bianconi, E. et al.: An estimation of the number of cells in the human body. Annals of Human Biology 40(6), 463–471 (2013). https://doi.org/10.3109/03014460.2013.807878; PubMed record: https://pubmed.ncbi.nlm.nih.gov/23829164/
• U.S. Geological Survey: The Water in You: Water and the Human Body. https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body