Water quality
![A rosette sampler is used to collect water samples in deep water, such as the Great Lakes or oceans, for water quality testing.](/Images/godic/202501/10/Rosette_sampler_EPA3701.gif")
![Urban runoff discharging to coastal waters](/Images/godic/202501/10/View_of_urban_runoff_discharging_to_coastal_waters3701.jpg")
![Satirical cartoon by William Heath, showing a woman observing monsters in a drop of London water (at the time of the Commission on the London Water Supply report, 1828)](/Images/godic/202501/10/Monster_Soup_commonly_called_Thames_Water._Wellcome_V00112183701.jpg")
![An automated sampling station installed along the East Branch Milwaukee River, New Fane, Wisconsin. The cover of the 24-bottle autosampler (center) is partially raised, showing the sample bottles inside. The autosampler was programmed to collect samples at time intervals, or proportionate to flow over a specified period. The data logger (white cabinet) recorded temperature, specific conductance, and dissolved oxygen levels.](/Images/godic/202501/10/WQ_sampling_station_USGS_20043701.jpg")
Water quality refers to the chemical, physical, biological, and radiological 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, safety of human contact and drinking water.