Characteristics and properties of waters - Pure water, natural waters

The commonplace nature of the water that surrounds us sometimes makes us forget that this liquid, which is so familiar to us, is in fact, thanks to its very special properties, both :

• a compound essential to life; in particular, water accounts for an average of 70-80% of the composition of living matter (but varies from 4% for resistant forms to over 98% for certain aquatic beings) and is the main constituent of the human organism:

  • three-day embryo: 94 to 97%,

  • newborn: 66-75%,

  • adult: 58 to 70%,

  • elderly: 55 to 60% ;

  What's more, on average, people cannot live without water for more than four days (there have been a few exceptions, such as after the January 2010 earthquake in Haiti);

• the most remarkably complex of all fluids: compared to most other substances, water presents a number of anomalies that will be discussed in this dossier.

After recalling the historical progression of human knowledge on the composition of water and the various meanings of the term (see Boxes 1 and 2), this article will review the composition, structure and main physico-chemical and biological properties of water, especially in temperature and pressure ranges close to ambient conditions, thus of interest to studies and applications relating to ecology, the treatment and distribution of drinking or industrial process water, sanitation, etc. It should be remembered that the thermodynamic properties of water in all its states and in all its fields of industrial use, over very wide pressure and temperature ranges (up to 1 GPa or 10 kbar and 2,500 K respectively), are the subject of another dossier in this Treatise [K 585v2] (see also [W 120] , archived). In what follows, we will successively examine :

• the composition and structure of the water molecule, focusing on two characteristics (dipole arrangement, hydrogen bonding) from which some of water's special physico-chemical properties derive (see also [RE 53] );

• the three states of water (solid, liquid, gaseous) and the differences in molecule organization in each of...