Water quality refers to the characteristics of a water supply that will influence its suitability for a specific use. Quality is defined by certain physical, chemical and biological characteristics and specific uses have different quality needs. For example, a lower threshold for salinity is applied to drinking water for human consumption based on health and aesthetic reasons than is applied to water used by stock. Similarly, the thresholds set for the suitability of water of a given salinity for irrigation varies depending on the sensitivity of the species of crop and the type of soil used for cropping.