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Well Water Safety

Contamination of Well Water

Pathways of Contamination

In aquifers, contaminants and recharge waters can follow similar pathways and can contaminate the groundwater in the following ways:

  • Contaminationspills on the ground (fuel and pesticide spills)
  • injection into the ground (septic leaching beds, poorly maintained wells, disposal of waste in wells)
  • improper handling of industrial solvents and chemicals (varsol and wood preservatives)
  • leakage from wastes (manure, wastewater, septic tanks and landfills)
  • leaking underground and aboveground fuel storage tanks
  • movement of groundwater between contaminated and clean aquifers
  • over-application of soil amendments such as manure, commercial fertilizers or pesticides.

Bacteriological Contaminants

Total Coliforms

What are Total coliforms?

  • Generalized group of bacteria found throughout the environment including soils, vegetation, and in human and animal feces.
  • Their presence may indicate a problem with your water supply, possibly through surface water contamination.
E. Coli

What is E. coli?

  • A group of bacteria that live in the intestines of warm-blooded animals
  • Their presence indicates recent fecal contamination such as sewage, and that there is a problem with your water supply.

Chemical Contaminants

Nitrates and Nitrites

  • Household SepticWhat are Nitrates and Nitrites?
    Nitrates and nitrites are inorganic chemicals. As a result of a chemical reaction ammonium is converted to nitrites and ultimately to nitrates. Nitrates are an important plant nutrient and type of inorganic fertilizer.
  • How Can Nitrates Enter My Well Water?
    Major sources of nitrate pollution that can affect well water include seepage from septic tanks and leaching beds, nitrogen based fertilizers and the presence of decaying plant matter and animal wastes. Wells are susceptible to nitrate contamination if they permit surface water to enter the well. Old, shallow and poorly constructed or maintained wells should be suspected.
  • Why Are Nitrates A Health Concern?
    A high nitrate content in well water can cause a condition in infants named Methemoglobinemia or "Blue Baby Syndrome." This rare but very serious condition affects the ability of blood to carry oxygen. Infants under the age of 6 months who consume baby formula prepared with high levels of nitrates are at greatest risk of acquiring this condition. Infants under six months of age lack enzymes, proteins which are important in chemical reactions in the body, to protect against methemoglobinemia.
  • What Level of Nitrites And Nitrates Are Acceptable In Well Water?
    The maximum concentration of nitrites in well water must not exceed 1.0 mg/L (ppm). Nitrates or combined levels of nitrates and nitrites must not exceed 10 mg/L (ppm).
  • What Should I Do If My Well Water Is Contaminated With High Levels of Nitrates?
    Do not use the well water for preparation of baby formula. In addition, do not boil your water as this will concentrate the nitrates/nitrites in the water. An alternative potable water supply should be used for infants under six months of age.

    Consider a water treatment device. Deionization, desalination and reverse osmosis units are capable of removing nitrate/nitrite contamination. It should be noted that bacterial contamination of a water supply often occurs in conjunction with nitrate contamination therefore, consider bacterial and chemical aspects of your well water quality prior to selecting a water treatment device.

Other Chemicals

Gas and Well

Fuels (Gasoline, Diesel, Heating Oil)

Any chemical or fuel spills that infiltrate the ground can contaminate your drinking water source. It only takes one litre of gasoline to contaminate 1 million litres of groundwater. Check that gasoline, pesticides, and other chemicals are stored in proper containers designed to help prevent spills or leakage. Don’t store these materials anywhere near your wells.

Remember the following

  • Refuel lawnmowers and other machinery a safe distance from the well.
  • Refuel over hard surfaces to help prevent infiltration of spills.
  • Change the oil in your vehicle on a sealed surface such as pavement or concrete away from the well.
  • Clean up spills with an absorbent material (clean sand or kitty litter) and remove to a Household Hazardous Waster depository. Keep a bucket nearby for quick access when spills occur.
  • Never hose down spills.


Contaminant sources affecting your well are most often found in your own backyard. Eliminate gardens adjacent to your well. Plant a permanent low-growing ground cover such as grass. Don’t use fertilizers or pesticides.

You should test for these if you are concerned about past or present use of pesticides near your well, if you’ve had a spill or leak, or if you are concerned about possible backflow through your plumbing into your well during mixing of pesticides.