Why We Measure Water Quality

Environment Canterbury has a legal responsibility to monitor the quality of groundwater and surface waters in the region. There are many reasons for doing this:

• Establish baseline conditions. Canterbury has vast water resources and there are many situations where little is known about the water quality. Understanding the current state of water quality is critical to managing it, and that almost always means taking measurements.
• Detect long-term trends. Often people become concerned that water quality at a particular place has deteriorated over time. Monitoring programmes often focus on identifying whether or not changes in water quality are occurring, because these may have the potential to affect the uses of that water.
• Determine suitability for uses. Water quality is frequently monitored to assess its suitability for specific purposes, such as swimming, source of drinking water, or as a habitat for fish and other aquatic animals. Measurements taken are usually compared against environmental guidelines. Such guidelines are generally expressed as numerical limits (such as concentrations of a contaminant) below which the water will be suitable for a particular purpose.
• Check compliance with standards. For some waters, water quality limits have been determined through a formal process, such as a regional plan or government regulation. When that happens, the limits become known as "standards", which must be met if the water is to be used for a specified purpose. For example, water that is to be used for drinking has to meet certain standards. Sampling results from Environment Canterbury's groundwater quality monitoring programmes are often measured against the New Zealand Drinking-water Standards 
• Assess adequacy of controls on discharges. Discharges of contaminants to water must be authorised by Environment Canterbury. When authorisations are given (usually as discharge consents) account is taken of the likely impact of the discharge on the quality of the receiving waters, based on knowledge of the water body at that time. Restrictions are placed on the discharge to limit any unacceptable water quality impacts. Additional monitoring improves our understanding of the resource and helps us to determine if those restrictions are still appropriate.
• Public confidence. As the authority with the responsibility for managing water quality in the region, Environment Canterbury is expected to know about the state of the resource, and how it may be changing, particularly as a result of human activity. The community needs to be reassured that its environmental guardian is out there, doing its job.