Water
The most ordinary molecule, with the strangest behavior
Ice floats, and that is strange: for almost every other substance, the solid is denser than the liquid. Scroll to cool this water from 25°C to −5°C and watch hydrogen bonds lock the molecules into an open lattice.
Liquid water: hydrogen bonds break and re-form within trillionths of a second, so molecules can pack closely.
Schematic: in real ice each molecule has 4 hydrogen-bonded neighbours; this flat projection shows 3. Dashed lines are hydrogen bonds.
Ice floats, and that is strange: for almost every other substance, the solid is denser than the liquid. Scroll to cool this water from 25°C to −5°C and watch hydrogen bonds lock the molecules into an open lattice.
Three questions this topic answers
Why does ice float instead of sinking to the bottom of a lake?
Inside a cell, is water just the background solvent, or an active player?
Is there any science behind “eight glasses a day”?
The 4°C secret
Drag the water temperature to see how density changes, and how much of an ice cube sits below the surface. The curve uses measured densities of pure water.
Because ice floats, lakes freeze from the top down, and the deepest water under the ice stays near 4°C, which is how fish survive winter. Ice at 0°C has a density of 0.917, far below anything on this chart.
Chapter manifest
Each chapter is stamped with the evidence level of its main claim. Chapter text is not written yet; this lists the plan.
- H2O-CH01
An anomalous molecule
Water’s 104.5° bond angle lets molecules link into a hydrogen-bond network, which explains floating ice and water’s high heat capacity.
Consensus 6 min In progress - H2O-CH02
Water in the cell is not just background
Protein folding and membrane formation both depend on how water pushes oily molecules together. Water takes part in the chemistry.
Consensus 8 min In progress - H2O-CH03
Water’s private channels
Aquaporins let water cross cell membranes quickly. Their discoverer, Peter Agre, shared the 2003 Nobel Prize in Chemistry.
Consensus 6 min In progress - H2O-CH04
How the body balances its water books
Thirst, antidiuretic hormone and the kidneys work together to keep body water within a narrow range.
Consensus 7 min In progress - H2O-CH05
Eight glasses and other myths
No original study supports “eight glasses a day”. Alkaline water, hydrogen water and “structured water” rest on very different evidence, and this chapter sorts them out.
Contested 9 min In progress - H2O-CH06
Your cells make water every day
The last step of mitochondrial respiration produces water.
↔ links to the other topicConsensus 5 min In progress
Three claims about drinking water
Pick whether you believe it, then see what the literature says. The full case is in chapter 5.
Everyone needs at least eight glasses of water a day.
A review tracing the claim found no study behind it. Food and other drinks also supply water, and for healthy adults in a mild climate thirst is usually enough. (Valtin 2002)
Drinking alkaline water changes your body’s pH.
Blood pH is held between 7.35 and 7.45 by buffers, the lungs and the kidneys, and anything you drink meets stomach acid first.
Water “remembers” substances once dissolved in it.
A widely publicised 1988 experiment could not be reproduced under controlled conditions, and no reproducible evidence supports “water memory”.
Key references
Each entry was checked against PubMed and links to the original by DOI.
- Ball P. (2017). Water is an active matrix of life for cell and molecular biology. Proc Natl Acad Sci U S A, 114(51), 13327–13335. How water actively shapes molecular biology, and why our understanding is still incomplete. Chapters 1–2. doi:10.1073/pnas.1703781114
- Agre P. (2004). Aquaporin water channels (Nobel Lecture). Angew Chem Int Ed Engl, 43(33), 4278–4290. The Nobel lecture by the discoverer of aquaporins. Chapter 3. doi:10.1002/anie.200460804
- Popkin BM, D’Anci KE, Rosenberg IH. (2010). Water, hydration, and health. Nutr Rev, 68(8), 439–458. Water intake, water balance and health, noting that long-term randomized trials are missing. Chapters 4–5. doi:10.1111/j.1753-4887.2010.00304.x
- Valtin H. (2002). “Drink at least eight glasses of water a day.” Really? Am J Physiol Regul Integr Comp Physiol, 283(5), R993–R1004. Traces “8 × 8” and finds no study behind it. Chapter 5. doi:10.1152/ajpregu.00365.2002