Sources of cyanide
  Cyanide is produced by the decomposition of some plants, can be present in some foods such as green almonds and improperly prepared cassava, and can be produced by some microorganisms. Cyanide is also used in the extraction of gold and silver from ores and in the electroplating, steel and chemical industries.
 
Types of cyanide
 In water, cyanide can be measured either as free or total cyanide.  Free cyanide consists of hydrogen cyanide (HCN) and the cyanide ion (CN-), which represent the more toxic forms of cyanide.  However, cyanide in water may be stably bound to metals such as iron. The total cyanide measurement shows the combined amount of both free and metal bound cyanide in the water.
 
Cyanide in drinking water
 In Australia, background levels of cyanide in drinking water range up to 0.05 mg/L, and are usually less than 0.02 mg/L.  
 
Short term health effects
 The World Health Organisation recommends that people should not consume water with a cyanide concentration above 0.5 mg/L for more than 5 days. This is to protect against short term health risks. This guidance is very conservative and includes a one hundred-fold safety factor.
 
Long term health effects
The Australian Drinking Water Guidelines 2011 recommend that drinking water contain less than of 0.08 mg/L of cyanide. This value is based on a lifetime of consumption, and is also a very conservative figure with large safety factors built into it.
 
References
 National Health and Medical Research Council (2011), Australian Drinking Water Guidelines 2011, Australian Government, Canberra, Australia.
 
World Health Organisation (2011), Guidelines for drinking water quality. World Health Organisation, Geneva, Switzerland.  
Page Updated: Friday 2 March 2012