ABSTRACT
The previous chapters have concentrated on the quantity of water and its variation over space and time. This chapter explores variations over space and time in the quality of water. Water quality is in fact rather difficult to define precisely, as “quality” is a value-laden term. Water that may be of acceptable quality for one use or function may be unacceptable for another. The term “water quality” therefore is usually taken to mean the physical and chemical characteristics of the water. Physical characteristics (or determinands) include the concentration of sediment in the water, the temperature of the water, and its colour. Chemical characteristics reflect the material dissolved in the water (as solutes) or held in the water on particles of sediment, and can be indexed by many different chemical determinands. Water has many unusual properties, including its ability to exist as vapour, liquid or solid, and its very high specific heat capacity. In terms of water quality, however, its most significant property is that virtually all substances can dissolve in it. This chapter first considers physical characteristics of rivers and lakes, before moving on to review chemical characteristics.
