Handbook of Environmental Engineering

11Water Quality

Steven C. Chapra

Department of Civil & Environmental Engineering, Tufts University, Medford, MA, USA

Water, water, everywhere, nor any drop to drink

“The Rime of the Ancient Mariner”Samuel Taylor Coleridge (1772–1834)

11.1 Introduction

Life as we know it on this planet would not be possible without the remarkable compound: water. In this regard, both the quantity and quality of water are critical. Anyone who has ever lived through a drought knows that having a sufficient water supply is of paramount importance to both humans and terrestrial animals as well as to the myriad organisms living in the aquatic environment. Similarly, anyone who has suffered through a flood recognizes that excessive uncontrolled water flow can be highly destructive.

Although an adequate and moderate water quantity is certainly essential, of equal importance is its quality. The quality of water can be conceptualized as its suitability (i) for particular human uses and (ii) for the support and health of organisms living within and in proximity to aquatic ecosystems. As expressed poetically by Coleridge, you can have plenty of water, but if it is unsafe to drink, you can die of thirst. Hence, ensuring adequate water quantity is futile without also considering water quality.

The quality of water is typically based on the water’s physical, chemical, and biological characteristics. Although the relationship of quality to these characteristics can be complex and multifaceted, water quality ...