Although we generally take water for granted, it is a remarkable chemical compound with unique properties that account for its essential life-supporting role. In this chapter, we will consider water from the perspective of those who drink it. First a question of aesthetics: What makes a glass of water pleasing to the eye and to the palate? There is more to water, however, than can be seen or tasted. Unseen impurities in water, depending on their identities and amounts, can impart a crisp, fresh taste or produce an unpleasant illness. And so, we next look at water as a solvent and at some of the things that may be dissolved in drinking water. How much of a substance dissolves in water makes concentration an important part of the story. The concentrations of substances dissolved in water can be expressed in several ways, including descriptions of the extremely low concentrations. To better comprehend aqueous solutions and why some substances dissolve in water while others do not, we will relate the properties of water molecules through such concepts as electronegativity, polarity, and hydrogen bonding.

Water dissolves various kinds of compounds, including those containing positive and negative ions, as well as some molecular compounds not composed of ions. We will consider the solubility of both types of substances and how it affects their presence in drinking water. Because the quality of drinking water is regulated by federal and state legislation, we will examine how drinking water is tested against standards, and how water is treated to make it potable (safe for drinking). Three case studies will give us the chance to look more closely at water quality. We examine the effect of calcium on water hardness, lead in water, and a particular category of compounds called trihalomethanes that are formed during water purification by chlorination. The questions posed early in the chapter about choices between tap water and bottled water are revisited. Finally, because most of the world's people do not have good access or choices for safe drinking water, we look briefly at ways to purify water, including home "filtration" systems, deionization, distillation, and reverse osmosis. And so, with water glasses or bottles raised, we extend the invitation to "take a drink."