According to Textbook Revolution, a student-run site “dedicated to increasing the use of free educational materials by teachers and professors,” "Here’s a comprehensive online-only book on the wet stuff, in a very well-laid out format. Frequently updated, searchable, and easy to browse. Highly Recommended!"

From the website itself: “Liquid water (H2O) is often perceived to be pretty ordinary as it is transparent, odorless, tasteless and ubiquitous. It is the simplest compound of the two most common reactive elements in the Universe. However, it is the most remarkable substance. Although we drink it, wash, fish and swim in it, and cook with it (although probably not all at the same time), we nearly always overlook the special relationship it has with our lives. Droughts cause famines and floods cause death and disease. We are about two-thirds water and, without it, we die within a few days. It has importance as a structured and structuring solvent, a solute, a reactant and a biomolecule. Life cannot evolve or continue without liquid water, which is why there is so much fuss about water being found on Mars and other planets and moons. Water is the second most common molecule in the Universe (behind hydrogen, H2) and is fundamental to star formation. It is unsurprising that it plays a central role in many of the World’s religions. Because of its clear importance, water is the most studied material on Earth but it comes as a surprise to find that its behavior and function are so poorly understood (or even ignored), not only by people in general, but also by scientists working with it everyday.”