How is water quality measured?

The presence of contaminants and the characteristics of water are used to indicate the quality of water. These water quality indicators can be categorised as chemical, physical and biological.

Chemical parameters

  • pH - a measure of the relative acidity or alkalinity of a substance
  • Dissolved oxygen – a measure of the volume of oxygen that is contained in water.
  • Total phosphorus - a measurement of all forms of phosphate compounds in a sample - orthophosphate, condensed phosphates and organically bound phosphates. Phosphorus is a nutrient essential to the growth of plants and animals.
  • Total nitrogen - a measurement of all forms of nitrogen compounds in a sample. A nutrient used primarily by plants and animals to synthesise protein. Nitrogen enters the ecosystem in several chemical forms and also occurs in other dissolved or particulate forms, such as tissues of living and dead organisms.

Physical parameters

  • Water temperature - a measure of the degree of hotness or coldness of a body of water. This can influence the amount of dissolved oxygen in the water.
  • Electrical conductivity - a measure of the physical ability of a sample to carry an electric current. Electrical conductivity is an indirect method of measuring salinity and includes the measurement of all salts and organic acids.
  • Turbidity - a measure of the cloudiness or muddiness of water. The greater the amount of total suspended and colloidal solids in the water, the higher the turbidity results.

Biological parameters

  • Aquatic macroinvertebrates or water bugs are animals that have no backbone, are visible with the naked eye and spend all or part of their life in water. They can be used as indicator species to determine water quality depending on their ‘sensitivity values’ (Streamwatch, 2012).
  • Vegetation on the riparian zones and macrophytes (water plants) can also be to determine river health and understand the influence on the physical and chemical parameters on the water way (Streamwatch, 2012).
  • Algae refer to a diverse range of photosynthetic organisms living in freshwater, most of which are harmless. However, some algae like blue-green algae produce toxins that are harmful to humans and animals if ingested through drinking water or come into contact with polluted water.