Drinking Water

The 2012 Great Lakes Water Quality Agreement states that “the Waters of the Great Lakes should be a source of safe, high quality drinking water”.

Status: Good
Trend: Unchanging*

* Trend based on Ontario data only

Assessment highlights

The overall status of treated drinking water sourced from Great Lakes surface waters is Good. Based on Ontario data from 2011 to 2020, the trend is Unchanging. A 10-year trend was not established for U.S. treated water quality because a revised approach was used which more accurately aggregates Great Lakes-sourced treated drinking water data from Great Lakes states. While this improves the assessment, a trend cannot be determined because the current data are not directly comparable with data used in past reports. A U.S. treated water quality trend for Great Lakes-sourced drinking water will be assessed in future reports. The waters of the Great Lakes continue to be a source of high-quality drinking water. As with all source waters, water from the Great Lakes must be treated to ensure it is safe to consume.

Ontario and U.S. state agencies have different monitoring protocols and reporting requirements regarding the quality of treated drinking water. Both countries compare microbial, radiological, and chemical parameters in treated drinking water to health-based standards. In the Province of Ontario, approximately 60% of the population is supplied with treated drinking water from the Great Lakes. In 2020, 99.8% of municipal residential treated drinking water quality tests met Ontario Drinking Water Quality Standards.

Of the 19.5 million U.S. residents served by the public water supplies that rely on the Great Lakes as their source water, 99.1% were serviced with drinking water that met all applicable health-based standards in 2020. While basin-wide treated drinking water is assessed as Good, localized exceedances of drinking water standards sometimes occur, impacting drinking water quality in those areas. Exceedances of drinking water standards can be caused by adverse source water quality, failure to treat properly, and inadequate water treatment and distribution infrastructure.

Bar chart displaying the trend of the percentage of treated drinking water tests meeting Ontario standards. For each year from 2011-12 to 2019-20, standards were met over 99.7 percent of the time.


Over 99.7% of Ontario municipal residential treated drinking water quality tests met standards each year between 2011-2020

Sub-indicator supporting the Drinking Water assessment


Lake Superior

Lake Michigan

Lake Huron

Lake Erie

Lake Ontario

Good and Undetermined

Good and Undetermined

Good and Undetermined

Good and Undetermined

Good and Undetermined

This indicator and overall assessment are based on treated drinking water information from both Ontario and the U.S., however Ontario treated water data are not available for individual lake assessments. To assess individual lakes, U.S. treated drinking water data and Ontario source water data are used. There were insufficient data to determine a 10-year trend for individual lakes.


Green indicator (good status). Most or all ecosystem components are in acceptable condition.
Yellow indicator (fair status). Some ecosystem components are in acceptable condition.
Red indicator (poor status). Very few or no ecosystem components are in acceptable condition.
Grey indicator (status indeterminate). Data are not available or are insufficient to assess condition of the ecosystem components.