Samples of water from the natural environment are routinely taken and analysed as part of a pre-determined monitoring programme by  regulatory authorities to ensure that waters remain unpolluted, or if polluted, that the levels of pollution are not increasing or are falling in line with an agreed remediation plan. An example of such a scheme is the harmonised monitoring scheme operated on all the major river systems in the UK. The parameters analysed will be highly dependent on nature of the local environment and/or the polluting sources in the area. In many cases the parameters will reflect the national and local water quality standards determined by law or other regulations. Typical parameters for  ensuring that unpolluted surface waters remain within acceptable chemical standards include pH, major cations and anions including ammonia, nitrate, nitrite, phosphate, conductivity, phenol, chemical oxygen demand (COD) and biochemical oxygen demand (BOD).