Properties of Water

Water is such a key element of life and everything we do that I thought I should pull together a page on the properties of water. Spurred on by making a steam boiler I thought I should pull some references together for this wonderful working fluid.

In the model engineering workshop we drink it, either as water from the tap or endless cups of tea, quench parts in it, clean items (main image shows paper backing of transfer being washed away), cool engines, dilute cutting fluid and use it as a working fluid in steam engines.

Water is distinguished from other common terrestrial substances in existing in all three phases at atmospheric temperatures and pressures.

The fundamental properties of water are listed below:

  • Density 998 (Ice: 917) kgm-3
  • Melting Point 273 K
  • Boiling Point 373 K
  • Linear expansivity (Ice: 5.0E-5) K-1
  • Specific heat capacity 4190 Jkg-1K-1
  • Latent heat of evaporation 2260000 Jkg-1
  • Thermal conductivity 0.591 Wm-1K-1
  • Refractive index 1.333 at 589.3nm 101.3kPa 0°C
  • Dielectric constant 80
  • Acoustic wave velocity (longitudinal bulk waves) 1498 ms-1
  • Bulk Modulus of Rigidity 2050000000 Nm-2
  • Surface Tension 0.0727 Nm-1
  • Viscosity 0.001 Nsm-2
  • Kinematic Viscosity 1.00200400801603E-06 m2s-1
  • Electromotive Series -1.23 V
  • Triple Point 273.16 K

Water is the only substance that expands on freezing as well as by heating and has a maximum density at 4°C.


A compound with all water removed, especially water of hydration.

Ethanol produced for fuel use is often referred to as anhydrous ethanol, as it has had almost all water removed.Examples: strongly heating copper(II) sulphate pentahydrate (CuSO4.5H2O) produces anhydrous copper(II) sulphate (CuSO4).

Atmometer – an instrument for measuring the rate at which water evaporates, also called an evaporimeter.

Brakish Water – water having less salt than sea water, but undrinkable, having salinity values ranging from about 0.5 to 17 parts per thousand.

Carbonate Water Hardness – Water hardness due to the presence of calcium and magnesium carbonates and bicarbonates. The “non-carbonate hardness” is due mostly to calcium and magnesium sulfates, chlorides, and nitrates

Drinking Water – water of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm.

electrolysis of water

Electrolysis of Water

The process for the electrochemical decomposition of water in a divided electrolytic cell by electrolysis. The result is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current being passed through the water.

Electrolysis – process for the electrochemical decomposition of water in a divided electrolytic cell by electrolysis. The result is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current being passed through the water.

Hardness – water contaminated with compounds of calcium and magnesium. Dissolved iron, manganese, and strontium compounds can also contribute to the “total hardness” of the water, which is usually expressed as ppm CaCO3. Water with a hardness over 80 ppm CaCO3 is often treated with water softeners, since hard water produces scale in hot water pipes and boilers and lowers the effectiveness of detergents.

Hydrophilic – a polar molecule or group that can form strong hydrogen bonds with water.

Hydrophobic – a nonpolar molecule or group that has little affinity for water. Hydrophobic groups on molecules in solution tend to turn in on themselves or clump together with other hydrophobic groups because they are unable to disrupt the network of strong hydrogen bonds in the water around them.


Able to absorb moisture from air.

Example: sodium hydroxide pellets are so hygroscopic that they dissolve in the water they absorb from the air.

Cloud condensation nuclei are typically hygroscopic, consisting of salts that produce aqueous solutions that have equilibrium vapour pressures less than those for pure water at the same temperature.


Formed when water is cooled below its freezing point.

Properties of ice:

  • Melting Point 273 K
  • Specific heat capacity 2100 Jkg-1K-1
  • Latent heat of fusion 335000 Jkg-1

Ice Point – the temperature at which pure ice can exist in equilibrium with water at standard atmospheric pressure.

Permanent Hardness – water hardness that remains after boiling the water, mainly due to dissolved calcium sulphate. Chlorides also contribute to permanent hardness.

Sour Water – waste waters containing fetid materials, usually sulphur compounds.

Steam – the gas phase of water.

Steam Point – the temperature at which pure water can exist in equilibrium with water vapour at standard atmospheric pressure.

Steam Quality – the percentage by weight of vapour in a steam and water mixture.

Temporary Hardness – the component of total water hardness that can be removed by boiling the water.

Triple Point – the temperature at which solid, liquid and vapour can exist together in equilibrium. For water this temperature is 273.16K

Water Hammer

Banging of pipes caused by the shock of closing valves – eg taps.

Occurs in a closed piping system as a result of the pressure being rapidly increased when the liquid velocity is suddenly increased.

This damaging effect is usually the result of sudden starting, stopping, change in pump speed, or the sudden opening or closing of a valve. Water hammer can usually be controlled by regulating the valve closure time, surge chambers, relief valves or other means.

Further Reading

Hopefully this has given a taster for the properties of water and for some of the terminology. This cannot cover everything as this is such a huge subject. However, I will add further references, notes and useful resources over time.

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