In contrast to the Prairies, natural groundwater quality in Central Canada is generally good, with low levels of dissolved minerals. Sand and gravel aquifers are found throughout the region as a result of glaciation, providing groundwater for many municipalities, rural residences, and farms. They are especially important in the heavily populated parts of southern Ontario east and west of Toronto, and throughout the St. Lawrence Valley in Quebec. An exception occurs in the southwestern Ontario clay plain, where many rural wells are only poorly supplied with groundwater from shale bedrock. Coarse sand and gravel deposits of glacial origin produce most groundwater in the rest of the region, although sandstone aquifers are also found extensively in eastern New Brunswick, Nova Scotia, and Newfoundland.
Most wells usually meet the needs of single domestic dwellings and farms.
Groundwater quality is relatively good in Atlantic Canada, though most water from bedrock aquifers tends to be hard. In some coastal areas aquifers are susceptible to sea water intrusion . The town of Shippegan in northeastern New Brunswick and the town of Pictou on Nova Scotia's north shore have had to abandon wells because of this problem. As well, arsenic is sometimes present in wells in Hants and Colchester counties of Nova Scotia.