Arsenic is a highly poisonous metalloid which can occur naturally in many sulfurous and metallic minerals. It may also be present in the water table due to direct soil or land contamination, especially in areas of aluminium production and where pesticide/herbicide spraying is practised. The single largest contributory factor to arsenic in drinking water supplies is diesel and petrol contamination off road surfaces (though to be in excess of 45% of total arsenic contamination), hence a private water supply by a major trunk road or motorway may prove to warrant investigation for this contaminant.
As a by product of the coal mining industry private water supplies located in mined or areas formerly mined may be higher risk.
Arsenic is a group 1 carcinogen meaning it has proven relationships in the development of some cancers, particularly skin and lung cancer. Recent research also illustrates a link between flu mutations and arsenic ingestion, with strains such as H1N1 being more prevelant in those areas with higher arsenic consumptions. The current WHO limit constitutes a risk of cancer of about 6 in 10,000 leading many countries such as the UK to insist on a lower permissable level.
Chronic arsenic poisoning from drinking contaminated water has been reported in concentrations as low as 0.17 parts per billion (0.0017 mg/l). It is therefore recommended that a suitable water treatment solution for drinking water is installed (typically an Reverse Osmosis system with activated alumina pre-filtration), if any detectable level is discovered.