of a substance, e.g. 30 mg/L of iron. It may also be a count such as 500 E. coli per litre or a statistical value such as the average concentration of copper is 2 mg/L. Many countries not only specify parametric values that may have health impacts but also specify parametric values for a range of constituents that by themselves are unlikely to have any impact on health. These include colour, turbidity, pH, and the organoleptic (aesthetic) parameters (taste and odour). It is possible and technically acceptable to refer to the same parameter in different ways that may appear to suggest a variation in the standard required. For example, nitrite may be measured as nitrite ion or expressed as N. A standard of "nitrite as N" set at 1.4 mg/L equals a nitrite ion concentration of 4.6 mg/L. This is an apparent difference of nearly threefold. Standards by country Australia Drinking water quality standards in Australia have been developed by the Australian Government National Health and Medical Research Council (NHMRC) in the form of the Australian Drinking Water Guidelines. These guidelines provide contaminant limits (pathogen, aesthetic, organic, inorganic, and radiological) as well as guidance on applying limits for the management of drinking water in Australian drinking water treatment and distribution. European Union The following parametric standards are included in the Drinking Water Directive and are expected to be enforced by appropriate legislation in every country in the European Union. Simple parametric values are reproduced here, but in many cases the original directive also provides caveats and notes about many of the values given. Acrylamide 0.10 μg/L Antimony 5.0 μg/L Arsenic 10 μg/L Benzene 1.0 μg/L Benzo(a)pyrene 0.010 μg/L Boron 1.0 mg/L Bromate 10 μg/L Cadmium 5.0 μg/L Chromium 50 μg/L Copper 2.0 mg/L Cyanide 50 μg/L 1,2-dichloroethane 3.0 μg/L Epichlorohydrin 0.10 μg/L Fluoride 1.5 mg/L Lead 10 μg/L Mercury 1.0 μg/L Nickel 20 μg/L Nitrate 50 mg/L Nitrite 0.50 mg/L Pesticides 0.10 μg/L Pesticides 0.50 μg/L total Polycyclic aromatic hydrocarbons 0.10 μg/L sum of concentrations of specified compounds Selenium 10 μg/L Tetrachloroethene and trichloroethene 10 μg/L sum of concentrations of specified parameters Trihalomethanes 100 μg/L sum of concentrations of specified compounds Vinyl chloride 0.50 μg/L United States In the United States, the federal legislation controlling drinking water quality is the Safe Drinking Water Act (SDWA) which is implemented by the U.S. Environmental Protection Agency (EPA), mainly through state or territorial