Sydney Catchment Authority constantly monitors its water quality by running it through a series of small aquaria each containing a small fish. The fishes respiration rate is monitored many time a minute and if a certain number of fish show abnormal respiration rates an alarm goes off. In addition to biomonitoring there are chemical electronic monitoring of water quality.<br><br>At the end of the system when used water is discharged after treatment Sydney water also uses oysters for bioaccumulation studies in receiving waters and uses ecotoxicology studies  on techniques on waste water of various dilutions. Conventional bucket chemistry is also done on waste water to set pollution control licences.  All this effort give Sydney some of the best and safest tap water in the world and our harbour and beaches are close to pristine.