Water Is Densest at Four Degrees, Not Zero
Water is the liquid essential to life. Its density peaks above freezing, which is why lakes freeze from the top.
Water is the transparent liquid that forms rivers, seas and rain, and is essential to all known life. One property makes life in cold climates possible: water is densest at about four degrees Celsius, not at freezing point. Colder water and ice are less dense, so they float — which is why lakes freeze from the surface down, leaving liquid water beneath where fish survive the winter. Almost every other substance is densest as a solid. *Water* is Old English, one of the oldest words in the language.
- The essential liquid. *Fresh water.*
- To supply water. *Water the plants.*
- Ice floats — an unusual property. *Ice floats.*
- H2O — the formula. *H2O.*
- Old English — *wæter*. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | water | Water. |
| Verb | water | Water it. |
| Adjective | watery | Watery. |
| Compound | waterfall | A waterfall. |
| Old English | wæter | Water. |
- The plants need water.Liquid.
- Ice floats because it is less dense.Physics.
- Lakes freeze from the top down.Consequence.
Unusual properties of water
- Densest at 4°C, so ice floats and lakes freeze downward
- High heat capacity, which moderates coastal climates
- High surface tension, letting insects walk on it
- A near-universal solvent, which is why it carries nutrients
- All of these follow from the hydrogen bonds between molecules
Old English *wæter*, of Germanic origin, from an ancient Indo-European root shared with Latin *unda* and Greek *hydor*.
Why does ice float?
Because water is densest at about four degrees Celsius. Below that it expands as it cools, so ice is less dense than the liquid.
Why does that matter?
Lakes freeze from the surface down rather than from the bottom up, leaving liquid water beneath where aquatic life can survive winter.