Copper is naturally present in the earth's crust and in seawater. Copper-containing fungicides are used to control biological growth in water supplies. A 0.3 mg/L copper limit for potable water has been established. Concentrations above 1 mg/L will impart a foul taste to water and can be toxic to fish. The measurement of copper is an important means of monitoring the corrosion of condensate systems and heat exchangers. CHEMetrics' test kits employ the bathocuproine reagent. Bathocuproine disulfonate forms an orange colored chelate with copper. The method measures total soluble copper as ppm (mg/L) Cu.