This is straight from the Indigenous Services Canada website
Roles and responsibilities Responsibilities for drinking water in First Nations communities in Canada are determined by location:
on reserves south of the 60th parallel in British Columbia in the territories On reserves south of the 60th parallel Drinking water quality management on reserves south of the 60th parallel is shared by:
First Nations communities the Government of Canada Chiefs and councils manage the day-to-day water and wastewater systems on reserves. This includes:
sampling and testing drinking water issuing drinking water advisories (DWAs) in their communities planning and developing facilities that provide the basic infrastructure needs of the community Indigenous Services Canada (ISC) provides funding and advice for water systems on First Nations reserves. For water systems, this includes:
design planning upgrading construction procurement commissioning operation and maintenance training and certification of operators ISC provides independent public health advice and guidance to communities and supports monitoring programs for drinking water quality. We:
provide advice when requested to community leadership when a potential concern about the drinking water quality is identified, by way of an Environmental Health Officer employed or funded by the Government of Canada
help First Nation communities address any unacceptable test results
support First Nations communities in establishing their own drinking water quality monitoring programs
Crown Indigenous Relations and Northern Affairs Canada also helps to helps to protect water quality in Canada's North and is responsible for managing water resources in and around Nunavut and some of the Northwest Territories. The Government of the Northwest Territories is responsible for the rest of the water in the Northwest Territories while the Government of Yukon is responsible for its water resources.
In consultation with the provinces and territories and other federal departments, Health Canada develops guidelines for drinking water quality. The Guidelines for Canadian Drinking Water Quality are used by every jurisdiction in Canada to establish drinking water quality requirements.