Characteristics and properties of waters - Pure water, natural waters

The ordinary 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 to 80% of the composition of living matter (though this ranges from 4% in some forms of resistance to more than 98% in certain aquatic organisms), and it is the main component of the human body:

  • three-day-old embryo: 94 to 97%,

  • newborn: 66 to 75%,

  • adults: 58 to 70%,

  • elderly: 55 to 60%;

  Furthermore, on average, humans cannot survive more than four days without water (although there have been a few exceptions where people survived longer, such as after the January 2010 earthquake in Haiti);

• the fluid with the most remarkable complexity: compared to most other substances, water exhibits numerous anomalies that will be discussed in this article.

After reviewing the historical development of human knowledge regarding 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 physicochemical and biological properties of water, particularly within temperature and pressure ranges close to ambient conditions, which are therefore relevant to studies and applications related to ecology, the treatment and distribution of drinking water or industrial process water, wastewater treatment, etc. It should be noted that the thermodynamic properties of water in all its states and in all areas of industrial use, across very wide ranges of pressure and temperature (up to 1 GPa or 10 kbar and 2,500 K, respectively), are the subject of another article in this database [K 585] (see also [W 120] , archived). In the following, the following topics will be examined in turn:

• the composition and structure of the water molecule, with a focus on two characteristics (dipole arrangement and hydrogen bonding) that give rise to certain unique physicochemical properties of water (see also [RE 53] );

• ...