Water Pollution — Definition

Definition

Water quality describes the physical, chemical and biological characteristics of water in relation to a specified use. Pollution occurs when contamination or altered conditions impair ecological function or suitability for use.

Clear appearance is insufficient evidence of safety because dissolved chemicals and microorganisms may be invisible. Two common indicators are dissolved oxygen, the oxygen present in water, and biochemical oxygen demand, the oxygen microorganisms require while decomposing biodegradable material under a defined test.

Their meanings differ, so a high value has different implications for each. Standards must be interpreted with their sampling conditions, units and intended water use.