Introduction to Water

Water (H2O) is the most abundant compound on Earth's surface. It covers approximately 70% of the Earth's surface and is vital for all known forms of life.

Although covering approximately 70% of the Earth's surface, most water is saline. Freshwater is available in almost all populated areas of the earth, although it may be expensive and the supply may not always be sustainable.

Sources from where water may be obtained include:

  • Ground sources such as groundwater and aquifers
  • Precipitation which includes rain, hail, snow, fog, etc
  • Surface water such as rivers, streams, glaciers
  • Biological sources such as plants
  • The sea through desalination
  • Water supply network


Parameters for water quality typically fall under three categories:

  • Physical: includes heavy metals, trace organic compounds and total suspended solids.
  • Chemical: includes heavy metals, trace organic compounds and total suspended solids.
  • Microbiological: includes coliform bacteria, E.coli and specific pathogenic species of bacteria. Chemical parameters tend to have a higher chronic health risk through the build-up of heavy metals in the water. Some components however, like nitrates/nitrites and arsenic, can have a more immediate impact on human health as well as the local environment. The presence of faecal coliforms (i.e. E.Coli) serves as an indication of contamination by sewage. Additional contaminants can also include Legionella, and viruses.


Water quality refers to the chemical, physical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which compliance can be assessed. The most common standards used to assess water quality relate to health of ecosystems, safe for human contact and drinking water.

Environmental water quality refers to water bodies such as lakes, rivers, and oceans. Water quality standards for surface waters vary significantly due to different environmental conditions, ecosystems, and intended human uses. The presence of toxic substances and high levels of certain microorganisms can present a health hazard for non-drinking water purposes such as irrigation, swimming, fishing, rafting, boating, and industrial uses. These conditions may also affect wildlife, which use the water for drinking or as a habitat.

Modern water quality laws generally specify protection of fisheries and recreational use and require, as a minimum, retention of current quality standards. Ideally, the return of these water bodies to pristine or pre-industrial conditions would be ideal. However, this would pose a significant challenge when considering that landscape changes (i.e. urbanisation) in and around many freshwater bodies have been the cause of current water quality standards.

Within Gibraltar, the Department of the Environment and the Environmental Agency work closely to ensure that healthy ecosystems are maintained locally, water quality standards improve where possible and human health is protected.