Nitrates are simply a combination of Nitrogen and Oxygen which occur naturally in every day foodstuffs and in many water supplies. At low levels, they pose no risk to human health. The EPA has set a standard of 10 milligrams per liter of water as the outer limit of safe.
Higher levels of nitrates in ground water do occur, and it is important to routinely test your well for the presence of elevated nitrate levels. Waste such as agricultural fertilizer, industrial waste, septic and sewage waste, etc. can seep into your ground water supply creating elevated levels of nitrates in your water supply.
Nitrate poisoning is most likely to occur in infants as is commonly referred to as "blue baby syndrome". The infant is actually asphyxiating due to oxygen shortage. Left untreated, this will cause brain damage and/or death. In adults, routine exposure to high nitrate levels have been linked with kidney and spleen damage.
Nitrates can be removed from your water using Reverse Osmosis Systems.
For more information on nitrates, visit the following websites: