In view of the quality of things deciding water quality, and also the good selection of variables used to describe the standing of water bodies in quantitative terms, it's tough to provide an easy definition of water quality. What is more, our understanding of water quality has evolved over the past century with the growth of water use needs and the ability to measure and interpret water characteristics.

QUALITY of the aquatic environment will be outlined as

• Set of concentrations, specifications, as well as physical partitions of inorganic or organic substances.
• The composition as well as state of aquatic accumulation within the water body.
• Description of temporal & spatial variations because of factors internal as well as external to the water body.

POLLUTION of the aquatic environment will be outlined as an introduction by man, directly or indirectly, of substances or energy that lead to such harmful effects as:

• harm caused to living resources,
• hazards caused to human health,
• hindrance caused to aquatic activities together with fishing,
• impairment of water quality with relation to its use in agricultural, industrial and sometimes economic activities, and
• reduction of amenities

The physical and chemical quality of pristine waters would unremarkably be as occurred in pre-human times, i.e. with no signs of anthropogenic impacts. The natural concentrations could, all the same, vary by one or additional orders of magnitude between completely different drainage basins. 

In practice, pristine waters are quite tough to seek out as a result of atmospherical transport of contaminants and their subsequent deposition in locations way distant from their origin.

Prior to pristine waters reaching the contaminated condition, two phases of water quality degradation occurs. Water quality problems have arisen because of the subsequent phases of activities. 

The first phase shows an alteration in water quality with proof of human impact however without any damage to the accumulation or restriction of water use. Such changes could solely be detectable by continual chemical measurements over very long time spans. 

The second phase consists of some degradation of water quality and attainable restriction of specific water uses because recommended water quality pointers (local, regional, or global) could also be exceeded. Once most acceptable concentrations for selected variables in regard to water use are exceeded, or the aquatic habitat and biota are markedly modified, the water quality is typically outlined as contaminated.

Description of the quality of the aquatic environment can be carried out in an exceeding sort of way. It will be achieved either through quantitative measurements, like chemical science determinations (in the water, particulate material, or biological tissues) and biochemical/biological tests (BOD measuring, toxicity tests, etc.), or through semi-quantitative and qualitative descriptions like organic phenomenon indices, visual aspects, species inventories, odour, etc. 

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