This technical bulletin is one in a series of 11 on well issues created for a person who is considering a new water supply well or who currently owns a water supply well. The purpose of this technical bulletin is to summarize the information on siting a well found in the Water Supply Wells Requirements and Best Management Practices manual published by the Ministry of the Environment and Climate Change.

Before choosing where to site a new water supply well, it is important to consider, several factors to protect drinking water from contaminants, including:

  • Potential sources of contamination (e.g. septic systems)
  • Safety (e.g. presence of overhead power lines or buried utilities)
  • Current and future building location(s)
  • Natural elements (e.g. ground surface, the flow of groundwater or the location of groundwater)

Regulation 903 (Wells Regulation), as amended, made under the Ontario Water Resources Act requires a person constructing a well to locate a new water supply well that:

  • meets minimum separation distances from sources of contaminants as described in the tables on page 4 of this technical bulletin,
  • is accessible for cleaning, treatment, repair, testing, inspection and visual examination at all times before, during and after completion of construction of the well, and
  • is at a higher elevation than the immediately surrounding area.

The minimum siting requirements are part of a multi-barrier approach to help reduce the risk of contaminants migrating into a new water supply well and allow a well to be accessible for maintenance, repair or abandonment.

Source of Contaminant

As guidance, "contaminant" and "source of contaminant" from the Environmental Protection Act are defined as follows:

means any solid, liquid, gas, odour, heat, sound, vibration, radiation or any combination of the above resulting directly or indirectly from human activities that causes or may cause an adverse effect.
“Source of contaminant”
means anything that discharges into the natural environment any contaminant.

Assessing and determining a potential "source of contaminant" is dealt with on a case by case basis.

A source of contaminants list includes, but is not limited to, the following:

  • Any sewage system
  • A farm animal feed lot
  • An animal manure pile
  • A barn and barnyard for domesticated animals
  • A lagoon
  • An underground or above ground storage tank designed for petroleum products or other organic chemicals
  • An open or closed hazardous or non hazardous landfill or dump
  • A sewer line
  • A fertilizer, pesticide, herbicide or other chemical storage area
  • A liquid or solid waste transfer facility
  • A sewage sludge or biosolids waste spreading or irrigation site

Best management practice considerations when siting a new well

Where possible, a water supply well should be located upgradient of potential sources of contamination such as a septic system. In some situations, the well owner and the person constructing the well should consider exceeding the minimum setback distance specified in the Wells Regulation for additional protection. For example, the separation distance should be increased:

  • Any time the natural features of the site indicate that contamination could travel easily and quickly to the water source.
  • If the well is going to be:
    • situated in a shallow aquifer,
    • set in highly fractured bedrock with overlying thin soil, or
    • located downgradient from a potential source of contamination.

The Wells Regulation specifies minimum separation distances from sources of contaminants but does not have a stated separation distance from a property line. Where practical, new wells should be located to at least a minimum setback distance applied from the well to all property lines because it is unlikely a well owner can control what happens on adjacent properties. The appropriate setback distance will be dependant on the type of well (e.g. deep drilled or shallow dug) and geologic conditions encountered.

Where complex geology exists that may increase the risk of contamination or contamination is likely to be encountered, it is recommended that a Professional Engineer or Professional Geoscientist be retained to site the well.

Further information on siting a new water supply well can be found in Chapter 4: Siting the Well of the Water Supply Wells Requirements and Best Management Practices manual.

Test holes and dewatering wells

New test holes and dewatering wells, as defined by the Wells Regulation, are exempt from the siting requirements in the Wells Regulation. These wells are not used for human consumption and many are designed to test, monitor or collect contaminated groundwater near a source of contamination. For further information on the construction requirements for test holes and dewatering wells see the Wells Regulation.

Additional information sources

This technical bulletin on well issues is one in a series of 11 created for owners of water supply wells which are available on the Water Supply wells: technical bulletin page.

A copy of the Water Supply Wells Requirements and Best Management Practices manual can be obtained from the Ministry’s web site.

A copy of the Ontario Water Resources Act, Regulation 903 as amended made under the Ontario Water Resources Act (Wells Regulation) and other legislation and regulations can be obtained from the e-Laws web site.

The publications are also available by calling the Publications Information Centre at 1-800-565-4923 or 416-325-4000.

For further information about wells, contact the Wells Help Desk at 1-888-396-WELL (9355) or the nearest Ministry of the Environment and Climate Change office listed in the blue pages of the telephone directory.

Notice: This bulletin is being provided for information purposes only and is not intended, nor should it be construed as providing legal advice in any circumstances. The applicable legislation including the Ontario Water Resources Act and Regulation 903, as amended and made under that Act, should be consulted. Legislation and regulations change from time to time so it is essential that the most current versions be used.

Table 1: Minimum horizontal separation distances between new wells and existing sewage systemsfootnote 2
 Well with watertight casing to a depth of ≥ 6m (19.7')Any other wellfootnote 1
Earth pit privy15m (50')30m (100')
Privy vault, pail privy10m (33')15m (50')
Greywater system10m (33')15m (50')
Cesspool30m (100')60m (200')
Treatment units (such as a septic tank)15m (50')15m (50')
Distribution pipe in a leaching or filter bed15m (50')30m (100')
Holding tank15m (50')15m (50')

These separation distances apply to any future earth pit privy, privy vault, pail privy, greywater system or cesspool, and a treatment unit, a distribution pipe in a leaching or filter bed, septic tank or holding tanks that has not been constructed but for which a building permit has been issued.

Table 2: Minimum horizontal separation distances between new wells and sources of contaminants other than those mentioned in Table 1
 Drilled well with casing that extends to a depth of more than 6 m (19.7')Any other wellfootnote 3
Source of contaminants15 m (50')30 m (100')

PIBS 7939e