Groundwater Quality & Quantity

Toronto and Region Conservation Authority (TRCA) monitors the quantity and quality of groundwater at various wells across the Region.

Groundwater is a vital resource — one that has been placed under increasing stress by overdrawing and contamination activities.

Approximately three million Ontario residents rely on groundwater from municipal and private wells as their primary source of drinking water. Many communities are dependent on groundwater supplies to maintain existing domestic, commercial, industrial, agricultural, and institutional operations.

Maintaining the flow between groundwater and surface water (known as recharge and discharge) is essential for a healthy watershed. Aquatic species rely on groundwater flowing into streams to preserve ecosystem functions.

What Are We Monitoring?

The Provincial Groundwater Monitoring Network (PGMN) was established in April 2000 to assess current groundwater conditions and provide an early warning system for changes in water levels and water quality.

PGMN is a partnership program between the Ontario Ministry of the Environment, Conservation and Parks and the province’s conservation authorities, as well as some municipalities in areas not covered by a conservation authority.

TRCA groundwater monitoring

There are almost 500 wells monitored across the province.

The role of the Ministry in the network is to set policy direction, develop strategic objectives and maintain the WISKI Webpro database.

TRCA is responsible for maintaining the data logger systems at 23 groundwater monitoring wells in our jurisdiction, collecting water level data, and arranging for chemical analyses of water quality samples at dedicated wells.

Of the 23 wells that TRCA monitored for water level data in 2020, a total of 16 groundwater wells were also sampled for water quality.

TRCA groundwater monitoring

The Province is currently exploring options to convert to a satellite telemetry system over the next few years, and TRCA currently has two wells that are set up in this new system.

TRCA’s groundwater level data and groundwater quality information, along with those of our municipal partners, are also uploaded to the Oak Ridges Moraine Groundwater Program website.

What Are The Data Telling Us?

Groundwater levels in the Greater Toronto Area (GTA) typically fluctuate within a range of 1 to 2 m in any given year, with higher groundwater levels during the spring and lower levels in summer months.

Select the image below to view our Groundwater Levels dashboard.

TRCA Watershed Reporting Hub Groundwater Levels dashboard

Of the wells TRCA monitors, only one shows a declining trend. However, this monitoring well currently has limited data and will require long-term data for more accurate interpretation. It is expected that this well may become stable in the near future.

Visit TRCA’s Watershed & Ecosystems Reporting Hub


TRCA Watershed Planning and Ecosystem Science: