E. coli - E. coli bacteria live only in the intestines of animals including humans. If any amount of E. coli bacteria is found in a water sample, it is an indication that human sewage or animal faeces has contaminated the water supply.
Nitrates - The presence of nitrates in well water is usually the result of farming activities like fertilizing, or seepage from septic systems. If nitrates are at levels above 10 milligrams per litre of water, an infant may suffer from a condition known as “blue baby syndrome” or methaemoglobinaemia. Blue baby syndrome is caused by the nitrates interfering with the blood’s ability to carry oxygen throughout the body.
Herbicides and Pesticides - Herbicides and pesticides from both agricultural and household use can contaminate wells if used improperly or excessively. Always read and use the amount stated on the manufacturer's label.