What are Threats?

There are many potential threats to municipal drinking water, but the level of risk they pose depends on the circumstances of the activity and its location.

The threats that pose the greatest risk to a municipal drinking water supply are called "significant threats."

A significant threat:

• Is located in a vulnerable area, usually close to a well or intake, and 
• Involves materials that have a high hazard rating.  

A material's hazard rating depends on these factors: 

• Toxicity: how dangerous it is to human health.
• Environmental fate: how quickly it moves through an aquifer. How quickly it may break down and become harmless.
• Quantity: how much is involved.
• Release to the environment: how easily it can get into the environment.
• Type of vulnerable area: where the activity is or would be located within a vulnerable area.

The Tables of Drinking Water Threats show where in a vulnerable area an activity must be located, and under what circumstances, for the activity to be considered a significant drinking water threat. 

We use these tables to identify significant drinking water threats in our assessment reports and to help develop source protection plan policies. 

Quality

• Waste disposal sites
• Sewage systems, including septic systems
• Storage, management and application of agricultural source material (e.g. manure)
• Handling, storage and application of non-agricultural source material (e.g. biosolids, food waste)
• Handling, storage and application of commercial fertilizers
• Handling, storage and application of pesticides
• Handling, storage and application of road salt
• Storage of snow
• Handling and storage of fuel (e.g. gasoline, home heating oil)
• Handling and storage of dense non-aqueous phase liquids (DNAPL, e.g. paint strippers, metal and plastic cleaning solvents, dry cleaning solvents)
• Handling and storage of organic solvents (e.g. dry cleaning solvents, paint thinners, glue solvents)
• Chemicals used in the de-icing of aircraft
• Livestock grazing, pasturing, outdoor confinement areas and farm-animal yards
• Establishment and operation of a liquid hydrocarbon pipeline

Quantity

• An activity that takes water from an aquifer or a surface water body without returning the water taken to the same aquifer or surface water body.
• An activity that reduces the recharge of an aquifer.