You can share your feedback on our best practices to protect sources of drinking water by emailing

Get started

We want to help you protect water sources and drinking water systems that are not included in a source protection plan or aren’t regulated by the Clean Water Act.

Protecting sources of drinking water is one part of Ontario’s strategy to ensure drinking water safety, sustainable water use and water security for future generations. You can tailor an approach that works for you.

By proactively protecting drinking water sources you:

  • protect human health and the environment
  • avoid the high costs of either cleaning up a contaminated drinking water source or having to find a new source of drinking water
  • reduce the cost of water treatment for some contaminants
  • extend the life of your system’s infrastructure
  • make informed land use planning decisions
  • increase public awareness and accountability of drinking water stewardship

Decide if you need to take action

Drinking water can come from surface water (an intake pipe or a shore well that draws water from a lake or river) and groundwater (a drilled or dug well) sources.

Certain activities can pose a risk to drinking water if pollutants are released to the environment. Pollutants, also called contaminants, are either:

  • chemicals, such as fuels, solvents, metals and pesticides
  • biological pathogens, such as bacteria and viruses

Soil can sometimes act as a natural filter for pathogens so some private well owners do not treat the water in their wells. But groundwater can become contaminated when chemicals or pathogens are released on or into the ground from human activity.

Example: Bacteria in private wells can come from on-site sewage systems and fuel can leak from heating oil tanks. Your well can become contaminated if these contaminants move through the soil into the groundwater.

Surface water bodies have no natural filter for contaminants like pathogens. Surface water can become contaminated when:

  • chemicals or pathogens are released directly into surface water bodies
  • surface water run off carries contaminants across land that drains into surface water bodies

As a result, surface water always needs some form of treatment before it is safe to drink.

Source protection adds another layer of protection by managing activities that may pose a risk before they become a problem.

If your drinking water source is not currently included in a provincially approved source protection plan, you may want to consider whether actions are needed to protect your drinking water source. You can learn more about how to identify areas where drinking water sources could be at risk and how to manage risks to drinking water sources.

Two things you’ll want to consider:

  • if your drinking water source is vulnerable to contamination
  • if other risk factors exist

Vulnerable drinking water sources

Some drinking water sources are more vulnerable to contamination than others, which means that you may need to take stronger action to protect them. Generally, the more vulnerable your source is, the more important it is to take action to protect the source.

Protecting the ground surface above vulnerable groundwater from potential contaminants will improve the protection of groundwater sources at deeper depths. Similarly, protecting the land that drains into surface water bodies from potential contaminants will improve the protection of the surface water source. If you determine your drinking water source is vulnerable to contamination, you may decide to take action to protect it.

The vulnerability of a drinking water source is based on the characteristics of the natural environment.

For groundwater sources, these characteristics include the type of soil and rock in the area and how quickly water (and contaminants) can travel through it.

For surface water sources, these characteristics include the type of source (lake or river), water flow and wind conditions, rainfall, the slope of the land, presence of vegetated or paved surfaces, and the soil type.

To help figure out how vulnerable your drinking water source is, you can look at:

  • Highly Vulnerable Aquifer mapping
  • your local setting
  • preferential pathways
  • other resources
  • hiring a professional

Highly Vulnerable Aquifers

Your aquifer is the layer of soil where your well gets its groundwater. Some aquifers are more vulnerable to contamination than others. 

Municipal groundwater studies and source water protection studies have been completed across much of Ontario. Highly Vulnerable Aquifers were delineated as part of the technical work in support of the development of source protection plans under the Clean Water Act. They are aquifers that can easily be contaminated because overlying soil layers are thin or permeable. They may or may not represent drinking water sources. Local source protection assessment reports will provide more information about how local Highly Vulnerable Aquifers were delineated and which aquifers are presented in the Highly Vulnerable Aquifer mapping. You can view Highly Vulnerable Aquifer mapping on the Source Protection Information Atlas. These maps can tell you where you may want to take action to protect your drinking water source.

Assess your local setting

Your local setting can tell you about the vulnerability of your drinking water source.

Groundwater sources

Take a look at the type of soil you have and how well the soil transmits water, also called the permeability of the soil. This relates to how quickly contaminants can reach your well from where they may have been released to the environment.

Soil is made up of particles of rock that can vary in size. The particles of rock that make up sand and gravel soil are larger than the particles of rock that make up silt and clay soil. Larger particles don’t pack together as well as small particles so there is more space between sand and gravel particles than silt and clay particles. Groundwater travels faster through sand and gravel than through silt and clay because there is more space between the larger soil particles to allow water to flow.

Look at infiltration for a very basic way to assess whether your surface soil is permeable. When it rains, does water pond on your property or absorb quickly into the ground? The answer can give you a sense of the type of soil in your area and how vulnerable your groundwater source may be.

Soil thickness can also help you determine how vulnerable your groundwater is. If you can see rock outcrops on your property or can’t dig very far before you hit rock, you have thin soil layers, which are usually more vulnerable than thicker layers.

You can get a rough idea of the vulnerability of your groundwater source as shown in the table below.

Local setting Vulnerability
Highly permeable surface sand and gravel, loose, mixed soil types over bedrock or shallow, fractured bedrock High
Lower permeable surface silt and clay or where impermeable soil is both above and below the aquifer as shown in your well log or geological maps Low

Surface water sources

You can look at the movement and circulation of the water in your lake, river or stream to assess the vulnerability of surface water sources. Gravity and wind action also both contribute to the movement and circulation of surface water bodies. For streams and rivers, the steeper the slope of the land, the faster the water moves downstream. Strong wind action can circulate water in a pond or lake.

You can get a rough idea of the vulnerability of your surface water source as shown in the table below.

Local setting Vulnerability
Slower moving water with less water circulation or mixing High
Faster moving water with more water circulation or mixing Low

Other factors affecting vulnerability

Preferential pathways, also called transport pathways, are human-made shortcuts that allow water to get to a drinking water source faster than under natural conditions. They can include things such as:

  • improperly constructed or abandoned wells
  • tile drains
  • pits and quarries
  • other excavations such as trenches for utilities and sewers

If you know these features are present, they can add to the vulnerability of your groundwater and/or surface water sources.

Preferential water flow also occurs through natural fractures in the soil and bedrock. These also impact vulnerability, especially when there is little soil overlying the bedrock. 

Vulnerability resources

Learning about the physical characteristics of your area can help with your assessment of vulnerability. These maps and resources provide information about soil types, aquifers and the steepness of the land. Through the Ministry of the Environment, Conservation and Parks, the Ministry of Natural Resources and Forestry and the Ministry of Energy, Northern Development and Mines’ OGSEarth website you can access:

  • water well records and other borehole records
  • quaternary geology and bedrock geology maps
  • aquifer maps
  • depth to water table maps
  • maps of the thickness of the soil layers above aquifers
  • geological cross-sections
  • topographic surface and surface water feature maps (topographic maps show the locations of hills, mountains and valleys using lines, called contour lines, to represent different elevations)

If you are located within a source protection area, the watershed characterization and assessment report within the local source protection plan are also good resources to learn more about vulnerability.

Hire a professional

You may need to do some further assessment work to determine how vulnerable your source is to contamination if you need more information than the simple techniques presented above. A basic hydrogeological assessment or advanced modelling techniques can be used to determine the vulnerability of your drinking water source. Hydrogeology, or the study of water underground, is an area of geoscience. Geoscience is a regulated profession in Ontario under the Professional Geoscientists Act. Hire a Professional Geoscientist or Professional Engineer who is qualified to conduct hydrogeological assessments to do this work for you.

Professionals can be found through local listings in your area. You can also view public registers of Professional Geoscientists on the Professional Geoscientists Ontario website and Professional Engineers on the Professional Engineers Ontario website.

Consider a risk-based approach

There may be other factors beyond vulnerability that are important for you to consider. A risk-based approach can help you decide whether it’s a priority for you to take action to protect your drinking water source. Municipalities and various communities may want to consider using this approach where information and resources are available.

The general concept of risk is the product of how likely something is to happen and how severe it would be if it happened. Risk is subjective, and your assessment of it may vary depending on your tolerance or comfort with accepting risk. Some level of risk is generally acceptable; however, it’s a value judgement often based on local circumstances. The risk of a drinking water source being contaminated or depleted can be determined by looking at risk factors.

Assess your risk factors

Think about your local situation and using the provided table, ask yourself some general questions to rank (low, moderate or high) how ‘at risk’ your drinking water source may be. High risk sources may warrant action to protect the source.

There is no right or wrong way to assess risk and no one factor is more (or less) important than another.

Example: Just because there are many wells in an area, doesn’t necessarily mean those wells are at risk.

You can look at many factors together to assess the overall risk and look at the importance of each risk question compared to each other. This relationship should be based on local knowledge and the reliability of the data you used to rank the risk. Assigning importance or weighting to each risk question can help determine an overall risk ranking.

Example: Confirmed water quality issues may be the driving factor where the system serves fewer users, whereas a system that serves many people where there are no known issues may still be at risk and require further protective actions.

You may also want to look at specific activities to determine the risk ranking.

Example: Residential septic systems may be a nearby activity that could pose a risk to the drinking water source. If these systems are not properly maintained, they may pose a higher risk due to potential contaminants being able to get into drinking water sources, even though residential activities are generally considered lower risk than commercial or industrial activities.

Risk questions Low risk Moderate risk High risk
How many wells or intakes are located in your area? A few Some Many
How deep are the wells and are they drilled or dug? Deep, drilled Intermediate Shallow, dug
How deep is the intake and how far is it located from shore? Deep, far Intermediate Shallow, nearshore
What is the vulnerability of your area? Low vulnerability setting Moderate vulnerability setting High vulnerability setting
How sensitive is the population? Healthy adults only Typical family or mixed range of ages Vulnerable populations like the elderly, youth or infants
How many people does the system serve? A few Some Many
How often is the system used? Occasional Seasonal or part time (work hours) Every day or only source
What types of activities are located nearby? Residential Agricultural Industrial or commercial
Do you have water quality issues? For example, algal booms or a boil water advisory. Confirmed none Possible / unknown Confirmed present
Are you located in an area where there is pressure for growth? Or are there other water supply and demand issues? No Maybe / unknown Yes
Is there oversight of the well(s) or intake(s)? For example, licencing, inspections, testing, compliance, and qualified operators. Yes Some None

Risk resources

The following data sources can help inform your risk factors and assessment of risk.

  • Property/lot fabric can give you a sense of how many people are located in your area based on township lot mapping but note that many vacant lots may be present in rural areas, which won’t be a good indicator of population density.
  • Development/building approval records, land use and zoning maps, official plans from your local municipality can help you determine the types of land use in your area.
  • Water Well Information System records can help with the assessment of the number and construction details of wells in your area.
  • Permit to Take Water records can be used to assess how much water is approved for use by permit holders (actual amounts used may be less).
  • Environmental Compliance Approval records through Access Environment can provide information on activities in your area that are regulated by the Ministry of the Environment, Conservation and Parks.
  • Vulnerability mapping from the Source Protection Information Atlas can give you vulnerability scores for locations within established source protection areas.
  • For information on water quality, drinking water quality and enforcement records, local health department records on water quality, hydrological/hydrogeological studies conducted by municipalities, conservation authorities or consultants, and available monitoring data from the Provincial Groundwater Monitoring Network or surface water monitoring stations can be accessed.

For municipalities

You can assess risk on a broader regional scale where multiple drinking water systems are present. For multiple systems, you can use risk factors to create a list of risk rankings for each system. Comparing risk rankings in a list may be useful to prioritize and justify deciding which systems need further actions to protect the source.

You can also consider the potential for future risk associated with potential future development.

Regardless of the assessment of vulnerability or risk, you may decide that further action is needed to protect the source.

Example: Even if a drinking water source is assessed to have low vulnerability and low risk based on current land uses, you can require technical work (or financial assurance to conduct such work) as a condition of development approvals with communal drinking water systems should the system become your responsibility in the future. You can learn more about managing risks to drinking water sources.

Work together

Protecting sources of drinking water is a shared responsibility. Think about your local situation and ask yourself “Is there a willingness in my community to protect the area around our wells or intakes?” Community/private drinking water may be from a shared source, and taking action in some circumstances might prove to be controversial.

Example: To manage risks from private septic systems, a septic inspection program could be implemented; however, this could impact property owners who have to pay for the cost of the inspections. Collaborating with neighbours at a larger scale can be even more effective than at a smaller/private property scale.

Setting up community meetings or social media platforms to discuss issues are some ways to engage various participants. Remember to include and be respectful of differing opinions and priorities. Various resources are available online to help with building partnerships and conflict resolution.

Coordination of actions to protect drinking water sources between different jurisdictions can also improve protection of drinking water sources. Many partnerships have already been established through implementation of source protection planning in Ontario under the Clean Water Act. Local expertise can help with implementation of the actions you want to take to protect your drinking water source. You can connect with the following groups to find out more:

  • municipalities
  • Conservation Ontario
  • conservation authorities
  • source protection authorities and committees
  • Risk Management Officials
  • Indigenous communities and organizations
  • environmental emergency response personnel
  • small businesses
  • agricultural operations
  • local and neighbouring watershed experts
  • environmental groups
  • other community partners

In addition, collaborating with others may yield information and data that you may otherwise not be aware of or have access to. Using existing source protection information along with other information sources can help inform local decisions and actions at all levels from individual to communal systems. The following resources can help you do this:

Having a clear project plan and collaborating with your community can ensure your actions to protect your drinking water source are successful.

Next steps

If you decide that you need to take action to protect your drinking water source, you can learn more about identifying areas where drinking water sources could be at risk, managing risks to drinking water sources, reviewing and evaluating your actions, and exploring your options to include your drinking water source in a source protection plan under the Clean Water Act.

If you decide that you do not need to take action, you may still want to consider some best practices to protect the environment, such as spill prevention measures, septic system inspections or outreach and education on proper well maintenance and annual fuel tank inspections. You can find resources in the manage risks to drinking water sources page.