E. coli

Escherichia coli (E. coli) is a type of bacteria found only in the intestines of humans and other warm-blooded animals. Its presence in drinking water indicates recent fecal contamination and may signal the presence of disease-causing microorganisms such as bacteria, viruses or parasites.

Total coliforms are a broader group of bacteria commonly found in the environment, including soil and vegetation. While total coliforms are not usually harmful, their presence indicates that a water supply may be vulnerable to contamination.

E. coli and total coliform bacteria enter drinking water through contamination from human or animal waste. Common sources include:

• domestic animals or wildlife
• improperly treated septic or sewage discharges
• leaching of animal manure
• poor well construction or poor well maintenance
• stormwater runoff
• surface water entering a well

During and after precipitation events, bacteria and other microorganisms may be washed into rivers, lakes or groundwater, increasing the risk of contamination.

E. coli and total coliform bacteria have a health-based guideline of non-detectable per 100 millilitres (100 mL). This means that no E. coli or total coliform bacteria should be present in any 100 mL sample of drinking water. Laboratory results may be reported using different terms, including:

• absent
• non-detect
• 0 CFU/100 mL
• less than one CFU/100 mL
• 0 MPN/100 mL

Laboratory testing is required to detect E. coli and total coliform bacteria. Regular testing of well water for bacterial and chemical parameters is recommended.

Testing requirements include:

• use of an SCC or CALA accredited laboratory
• collection of samples using sterile bottles provided by the laboratory
• keeping samples cool
• delivery of samples to the laboratory within 24 hours of collection

For more information on water testing services, please see: Well water testing. Testing costs vary depending on the laboratory and the number of parameters analyzed.

Exposure to disease-causing microorganisms in drinking water may result in waterborne illness. Common symptoms include:

• diarrhea
• nausea
• vomiting

Infants, older adults and people with weakened immune systems may experience more severe effects. In rare cases, illness may affect organs such as the kidneys, liver, nervous system, lungs, skin or eyes.

Health risks occur through ingestion only, including:

• drinking
• cooking
• brushing teeth

When E. coli or total coliform bacteria are detected, drinking water is not considered safe. A second test is recommended to confirm the result.

While awaiting confirmation, exposure can be reduced by:

• boiling water before drinking or food preparation
• using bottled water or another tested safe water source

To destroy bacteria, water must be kept at a rolling boil for at least one minute. Boiling is not required for laundry or dishwashing. Showering and bathing may continue if water is not swallowed. Infants and toddlers should be sponge bathed.

If E. coli is confirmed, the source of contamination should be identified and corrected.

Bacteria cannot be removed using standard pitcher-style carbon filters.

Effective treatment methods for microbial contamination include:

• permanent point-of-entry disinfection systems using chlorine, ozone or ultraviolet light
• distillation

Ultraviolet treatment systems must be certified to NSF standards 55 Class A for pathogen inactivation. These systems require clear water and may require pre-filtration if water is cloudy.

After installation, drinking water should be re-tested to confirm the system is working properly. For water supplies affected by bacterial contamination, testing every three months is recommended.

Preventive measures reduce the risk of bacterial contamination and include:

• disinfecting any water added to the well
• disinfecting the well, pump and plumbing after repairs
• ensuring the well has a vermin-proof cap
• keeping well equipment off the ground during maintenance
• maintaining a watertight well casing that extends above ground
• preventing surface water from entering the well

Provincial regulations set minimum separation distances between wells and potential sources of contamination to reduce the risk of bacteria entering drinking water supplies.

Water Well Regulation 90-79 (Clean Water Act)

Cesspool receiving raw sewage

• all well types: minimum distance of 30 metres

Seepage pit, filter bed, soil absorption field, earth pit privy or similar disposal unit:

• drilled well: minimum distance of 25 metres
• dug well: minimum distance of 30 metres

Septic tank, concrete vault privy or sewer of tightly jointed tile or equivalent material, including sewer-connected foundation drains:

• drilled well: minimum distance of 15 metres
• dug well: minimum distance of 30 metres

Sewer of cast iron with leaded or approved mechanical joints, independent clean water drain or cistern:

• all well types: minimum distance of three metres

Pumphouse floor drain, cast iron with leaded or approved mechanical joints, draining to ground surface:

• all well types: minimum distance of 600 millimetres

Cesspool or seepage pit more than 3.5 metres deep, unless the well is cased to prevent seepage into the well:

• all well types: minimum distance of 60 metres

Right-of-way of any highway or public road:

• all well types: minimum distance of 10 metres

Septic tank:

• drilled well: minimum distance of 15 metres
• dug well or sandpoint well: minimum distance of 30 metres

Disposal field:

• drilled well: minimum distance of 23 metres
• dug well or sandpoint well: minimum distance of 30 metres