Water is probably the most eccentric chemical known to man. It is the only substance which exists in all three states of matter on this planet and it is also the only inorganic liquid which occurs naturally. On the other hand it is the natural substrate for all in vivo processes and the lifelong environment for many species.

It has long been a source of wonder for philosophers, painters, poets, composers and, much more recently, for physicists, chemists, biologists, and even astronomers. Although there is now general agreement that its remarkable properties derive from hydrogen bonding, we are still at a loss how to explain the bulk physical properties in terms of the molecular structure of the H2O molecule or, indeed, the water dimer. Intensive study of water dates from the 1960s, after the foundation had been laid by Bernal and Fowler in their classic paper of 1933. The realization that water plays a central role in maintaining native biopolymer structures was slow in coming, but since 1970 the importance of hydration figures largely in the protein literature.

Over a period of thirteen years I was involved in the publication of the seven-volume work Water – A Comprehensive Treatise. For various reasons both of a personal and practical nature, I decided not to continue with this project. On the other hand, there are still many topics where water takes a central position and which are due for a review. There are also other topics which featured in the Comprehensive Treatise but where recent progress has been so rapid that an update is opportune.