Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through treatment of the water, can be assessed. The most common standards used to monitor and assess water quality convey the health of ecosystems, safety of human contact, extent of water pollution and condition of drinking water. Water quality has a significant impact on water supply and oftentimes determines supply options.
The health impact of water is mainly due to pathogens. However, dissolved substances can sometimes have an effect. Due to arsenic contamination of groundwater W, the acute effect of bacterial disease has been replaced by a slower health problem - probably better than a quick death from cholera, but very serious nonetheless.