Private Wells

Learn more about free well water testing for bacteria

Where water comes from

The water we drink generally comes from surface water (above ground) or groundwater (underground). Only about 1% of the Earth's water is surface and groundwater.

The water cycle: Rain or melting snow can take several paths. It can runoff into streams, lakes or rivers. It can seep into the ground to be used directly by plants or to recharge groundwater. It can evaporate and return to the atmosphere. The cycle is complete when water in the atmosphere returns to earth as rain or snow. Groundwater from a deep well may have been in the ground for hundreds or thousands of years. In a shallow aquifer, the water may be a few weeks or years old.

The hydrologic cycle

 The hydrologic cycle showing how rain or snow runoff pools underground to provide water

How water moves

Groundwater flows from areas of higher elevation and/or pressure to lower elevation and/or pressure. It can flow horizontally or vertically upward or downward but usually in just one direction. This direction of natural flow can be affected or changed by pumping a well. How fast groundwater moves depends on how porous the soil or rock is, and whether the groundwater surface is sloped. The speed of water movement varies greatly.

The water table: The point at which the ground is saturated determines the water table. This level rises and falls depending on rainfall and local water use. Taking water out of the ground faster than it is recharged by the water cycle will lower the local water table.


Is it clean? When an aquifer gets contaminated, the water may be unfit and unsafe to use. Groundwater can become contaminated in several ways:

  • spills on the ground, e.g., fuel and pesticide spills
  • injection into the ground, e.g., septic leaching beds, disposal of waste in wells, contaminated surface water running into poorly constructed or maintained wells
  • improper handling of industrial solvents and chemicals
  • waste leakage, e.g., manure storage, wastewater, septic tanks and landfills
  • leaking underground and above-ground fuel storage tanks
  • groundwater travelling from contaminated to clean aquifers
  • over-application of manure, commercial fertilizers or pesticides

Whether the groundwater gets contaminated depends on:

  • the size or strength of the contamination source
  • the ease with which the contaminant can move into or travel through the soil
Types of wells

There are over 50,000 private wells in the Ottawa area. Well owners are responsible for ensuring that water from their wells is safe to drink, and that their wells are not contaminating the groundwater. Wells must be properly designed and maintained to ensure that drinking water is safe.

Common types of wells: Dug and bored wells (with casings 60 to 120 cm/24 to 48 in.) are less expensive to install than drilled wells. Like sand point wells, dug/bored wells are prone to near-surface contamination and shortages. Drilled wells (casings 10 to 20 cm/4 to 8 in.) cost more but penetrate deeper aquifers.

Drilled wells

Cross cut image of a drillled well

A drilled well consists of a small-diameter casing ranging in size from 10 to 20 cm (4 to 8 in.). 
Drilled wells obtain water from either overburden or bedrock aquifers. Overburden wells include those constructed into overburden aquifers (the geological materials above bedrock), composed typically of sands and gravels, but also possibly of silts and clays.

A properly constructed and maintained drilled well should prevent the entry of any foreign substance into the well casing that might impair water quality.



Dug wells  

Cross cut image of a dug well

Dug wells are constructed with prefabricated concrete tile or corrugated galvanized steel pipe ranging in diameter from 60 to 120 cm (24 to 48 in).  Older wells may be constructed of brick, stone or even wood cribbing and are very susceptible to undesirable surface-water seepage through the portion of the casing located above the water table.  Dug wells, which were often hand-dug in the past, are now constructed primarily with excavation equipment

and are usually no more than 9 m (30 ft) deep.  

Sand Point Wells

Cross cut image of a sand point well

Sand point well point or driven-point wells consist of a small-diameter casing ranging in size from 2.5 to 5 cm (1-2 in.). Well points are constructed in sand and gravel aquifers and are either driven or jetted (inserted using high-pressure water) into the ground.  Well points are usually only installed where the aquifer has a shallow water table and contains few or no stones. 




Source: Ontario Ministry of Agriculture, Food and Rural Affairs.

How well water gets contaminated

Your well water can be contaminated by:

  • openings in the well seal
  • improperly installed well casing
  • well casing not deep enough
  • well casing not sealed
  • a source of contamination not related to well construction (e.g. your septic system, pet waste or livestock waste, agricultural or road chemicals)

You can prevent contamination by:

  • do not allow liquids or wastes from garbage and manure piles to drain towards the well casing
  • do not locate dog runs around the well casing
  • do not treat the area around the well with pesticides or fertilizer
  • do not flush oils, detergents, paints, solvents or other chemicals down the toilet

Proper installation and maintenance includes ensuring the:

  • sanitary seal or well cap is securely in place and watertight
  • cap is at least 30 cm above the ground
  • joints, cracks and connections in the well casing are sealed
  • surface drainage near the well is directed away from the well casing
  • surface water does not pond near the well
  • well pump and distribution systems are checked regularly
  • changes in the quantity and quality of water are investigated immediately
  • well water is tested for bacteria three times a year and after major plumbing work
  • wells are chlorinated and tested after any major repairs

Abandoned wells should be carefully sealed to prevent pollution of groundwater and any safety hazards. Hiring a qualified well contractor to seal the well is strongly recommended. 

Well water problems and solutions
Common water quality problems, possible causes and treatments
ProblemPossible CauseTreatment
Health effects: diarrhea, stomach cramps Bacteria, parasites, viruses
  • Chlorination/filtration method
  • Ultra-violet systems
  • Chlorination - injector units
Methaemoglobinemia (blue baby syndrome) Nitrate Reverse-osmosis units
High blood pressure Sodium Reverse-osmosis units
Scale build-up in kettles and water heaters. Soap scum, bathtub ring Hardness (hard water) Water softeners
Red to brown slime in toilet tanks; iron staining; unpleasant taste or odours Iron bacteria Chlorination/filtration units
Rusty black stains on fixtures, laundry Iron and/or manganese Filtration; greensand filters; water softeners; chlorination/filtration units
"Rotten-egg" smell and taste Hydrogen sulphide and/or sulphate reducing bacteria Chlorination/filtration units; greensand filters; aeration
Water has laxative effects Sulphate Reverse-osmosis units
Salty taste, corrosive Chloride Reverse-osmosis units
Gassy smell, gas bubbles escaping from water Gases (methane) Aeration; activated carbon filters
Cloudy water Turbidity (clay) Filters; alum treatment

Other sources of drinking water

Bottled water

While bottled water available in Canada is generally of good quality, it is not necessarily safer or healthier than water from municipal supplies.

The sale of bottled water is not licensed in Canada. However, the federal Health Protection Branch makes spot checks from time to time of both domestic and foreign bottled water. In addition, local health units do regular bacterial testing on all bottled water distribution located in their district.

Municipal water supplies are checked for 350 or more substances. Only three substances must be checked in bottled water. These are bacteria content, fluoride and total dissolved solids (magnesium, iron, sodium).

Bottled water may contain naturally occurring bacteria, which under improper and/or prolonged storage conditions, could increase in numbers to levels that may be harmful to health. Refrigeration is a good way to reduce the growth of these bacteria.

Storage of bottled water may provide an opportunity for bacteria to grow, particularly if the containers were not sterile.

Water from cisterns

The water in cisterns usually comes from rainfall collected off the roof. It is stored in concrete tanks (reservoirs) in the basement or attic.

The water collected can be contaminated from many sources (especially bird droppings) and thus is not safe for drinking.

If a cistern supply exists or is planned, it is recommended that no connections be made between the main water supply and the cistern. Colour coding of the water pipes is also a good idea to ensure that a separation exists.

The use of a cistern supply is not recommended for human bathing or drinking water. Cistern water should only be used for such uses as lawn and garden watering and washing cars.

Private wells - Drinking water safety during and after a power outage

Power outages can disrupt private well water drinking supplies. Visit our Severe weather page for more information.

Testing for sodium and nitrate

Public Health Ontario provides testing for E. coli and total coliforms for private well owners. For all other environmental testing, including sodium and nitrate, private well owners must contact a private lab.


Are you on a salt restricted diet for a medical condition such as very high blood pressure or congestive heart failure? Do you have a baby that requires salt restriction that you are feeding with powdered formula made from your private well water?

If you have one of the above medical conditions, it is important to speak with your physician to determine whether you need to an alternative drinking water source.

You should be aware of the amount of sodium in your drinking water - the advisory level for sodium in drinking water is 20 mg/L (milligrams per litre). This advisory level is for people on sodium-restricted diets. Typically one can taste sodium at 130 to 140 mg/L, and when it exceeds 200 mg/L, water tastes salty. Keep in mind that there are many other sources of sodium - such as processed foods and, in some homes, water softeners—that are usually much larger contributors to your daily sodium intake such as processed foods.  The amount of sodium in City of Ottawa supplied water from the Ottawa River is low (18 mg/L) and would not be a health concern to people on sodium-restricted diets. However, well water usually has a higher sodium content than river or lake water.  

If your water is supplied from one of Ottawa’s municipal well systems (Carp, Kings Park, Munster, Shadow Ridge, Vars, Richmond West) the sodium levels are as follows (original data from Drinking water - City of Ottawa):

Well systemSodium (mg/L)
Carp 57
Kings Park (Richmond) 90
Munster 78
Shadow Ridge (Greely) 70
Vars 32
Richmond West Well System 36
Taken from the specific well system’s 2022 Annual Report on Drinking Water Quality; sodium is tested every 5 years.

If you have your own private well, you should consider testing your water for sodium at least once every 5 years.  As well, it is highly recommended to have your water tested for nitrates (important for babies receiving formula made with water from your private well). Contact a private lab that tests drinking water for sodium and nitrates.

Do you have a water softener? Water softeners can substantially increase the level of sodium in drinking water. Use a separate, soft water supply (one that by-passes the water softening equipment) for drinking and cooking purposes as some foods already have a high sodium content.  


What is nitrate?

Nitrate is a form of nitrogen that is found naturally in groundwater and in plants such as fruits and vegetables.  Other sources include fertilizers, industrial waste water and septic system leaks.

How do nitrates get into drinking water?

Nitrates can get into groundwater and into your well water through many sources, including: surface runoff from agricultural activities like fertilizer use from farming or animal manure, into a poorly constructed or damaged well; leaking septic systems; and the natural decay of organic matter in groundwater. Elevated concentrations of nitrate in groundwater are often localized and due to human activities. This means that you could have high nitrate in your water even if your neighbour does not.

What are the health effects of nitrate in drinking water?

For most Ontario residents, the primary source of nitrate exposure is through food, followed by drinking water. Consuming high levels of dietary nitrates can be harmful especially for infants under six months of age. Exposure to high concentrations of nitrate can cause a condition called methemoglobinemia also known as blue-baby syndrome. Methemoglobinemia interferes with oxygen delivery to cells in the body. The most obvious symptom is bluish skin colour, particularly around the eyes and mouth.

There is also some evidence linking nitrate exposure to adverse pregnancy outcomes; pregnant women can also be considered a special risk group.

How do I know if I have nitrate in my drinking water?

Nitrates are tasteless, odourless and colourless. Municipal drinking water systems are tested regularly but the only way to know if there are nitrates in your private well water is to have it tested by a licensed laboratory

You should test your private well for nitrate:

  • At least twice initially – once in the spring and once in the fall because concentrations will vary with weather and the season
  • More frequently if nitrate levels are near the drinking water standard or if you have a dug well (less than 6 m deep)
  • If your well always shows no signs of nitrate, you can test less often (every 2 to 3 years)
  • If you have a treatment system to remove nitrate from your water, test the treated water annually to ensure it is working properly. 
How much nitrate is allowed in drinking water?

The maximum acceptable concentration for nitrate (as nitrogen) in drinking water in Ontario is 10 mg/L. This amount is set to be protective of the health of the most vulnerable subpopulation, formula fed infants.

What should I do if I have nitrates in my drinking water?

You are responsible for ensuring your well water is safe to drink.  If your well water has levels of nitrate above the Ontario standard and there is an infant (under 6 months) or a pregnant woman in the home, you should use another source of water for drinking and preparing food (including formula). Boiling water will not reduce or remove nitrate. Other steps you could take include:

  • Seek advice from a licensed well contractor or a licensed groundwater consultant to ensure your well is properly constructed and maintained to minimize the risk of contamination;
  • Identify sources of nitrate contamination, such as fertilizers, septic tanks, manure, etc., around your property and reduce entry into your well;
  • Remove or reduce potential sources of nitrate near the well;
  • Consider options for a long-term safe water supply, such as obtaining water from a public (municipal) water system or installing a water treatment system. For treatment options, you should consult with a water treatment professional;
  • Regularly inspect your well and test your well water. Hire a licensed well contractor if needed.

Groundwater research

East Ottawa – Champlain Groundwater Study

 More information


Ottawa Public Health - Tel: 613-580-6744 Interpretation of well water results
Public Health Ontario Laboratory, 2380 St. Laurent Blvd - Tel: 613-736-6800 Well water testing
Ministry of Environment, Conservation and Parks - Tel: 1-800-565-4923 Well records, permits, construction, maintenance, and abandonment
Ministry of Environment, Conservation and Parks directory of licensed well contractors Drilling, servicing, consultation


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