Water is the material cause of all things (Thales, 624–546 bc).
Water is a unique, ubiquitous substance that is a major
component of all living things. Its nature and properties
have intrigued philosophers, naturalists and scientists since
antiquity. Water continues to engage the attention of
scientists today as it remains incompletely understood in
spite of intense study over many years. This is primarily
because water is anomolous in many of its physical and
chemical properties. Some of water’s unique properties are
literally essential for life, while others have profound
effects on the size and shape of living organisms, how they
work, and the physical limits or constraints within which
they must operate. This was recognized by Lawrence
Henderson in 1913 in his classic and still very readable
book, The Fitness of the Environment: An Inquiry into the
Biological Significance of the Properties of Matter. Since
then more has been learned about the structure and
properties of water at the molecular level, much of it
through spectroscopic and thermodynamic experiments.
The more recent discipline of computer simulation has also
played a role, having achieved a level of sophistication in
the study of water in which it can be used to interpret
experiments and simulate properties not directly accessible
by experiment. Many of water’s basic physical properties
can now be explained, at least semiquantitatively, in
molecular and structural terms.