Water quality is defined in terms of the chemical, physical and biological content of water. The water quality of rivers and lakes changes with the seasons and geographic areas, even when there is no pollution present. There is no single measure that constitutes good water quality. For instance, water suitable for drinking can be used for irrigation, but water used for irrigation may not meet drinking water guidelines. The quality of water appropriate for recreational purposes differs from that used for industrial processes.
Good water quality
Good quality drinking water is free from disease-causing organisms, harmful chemical substances, and radioactive matter. It tastes good, is aesthetically appealing, and free from objectionable color or odor.
It should be noted that there is a difference between "pure water" and "safe drinking water". Pure water, often defined as water containing no minerals or chemicals, does not exist naturally in the environment. Under ideal conditions, water may be distilled to produce "pure" water. Safe drinking water, on the other hand, may retain naturally occurring minerals and chemicals such as calcium, potassium, sodium or fluoride which are actually beneficial to human health and may also improve the taste of the water. Where the minerals or chemicals occur naturally in concentrations that may be harmful or displeasing, then certain water treatment processes are used to reduce or remove the substances. In fact, some chemicals are actually added to produce good drinking water; the best examples of chemical addition are chlorine used as a disinfectant to destroy microbial contaminants, or fluoride used to reduce dental cavities.
Bad water quality
There are many factors which causes bad water quality, those which may affect the growth of plants are:
Sewage Pollution - Harmful chemicals may be release together with the sewage.
Oil and other chemicals - Toxic to aquatic life and plants.
Detergents - Toxic to aquatic life, which decrease the amount of nutrients in the water for the plants.
Weeds - Takes in nutrient in the water > lesser nutrient in water > lesser nutrient for other water plants.
Litter and rubbish - Encourages weed growth.
Upper Parramatta River Catchment Trust (2001) Causes of poor water quality
CSREES Florida water quality programme(November 20 2007) Water quality