It can damage the nervous system and is a known carcinogen, responsible for lung, skin and reportedly also intestinal cancers. It is a teratogen, meaning it can enter the metabolic system of unborn children. Its actual toxicity depends on such factors as general health and diet. It accumulates in the body and passes slowly out through hair and nails. Inhalation, ingestion, and skin contact are the primary routes of human exposure to arsenic.
Ingestion is a hazard for everybody.
Not only water, but much food contains small amounts of arsenic. There is debate on how much arsenic the human body can handle without being harmed. Some say 0.012 milligrams per day. The US Environmental Protection Agency is also expected to adopt this recommendation. This is 1,000 times the recommended limit.