The capacity and extent of most aquifers is not known precisely, and hydrogeologists can only estimate the amount of water stored underground. Current work by the Ontario Geological Survey and the Geological Survey of Canada may shed more light on this question.
A further problem is that even when aquifers are identified, there is no uniform protocol for naming them, as noted by staff at the Geological Survey of Canada.
The ad hoc approach currently applied by consultants and municipalities to the naming of aquifers...can lead to unnecessary confusion and additional work in attempting to identify the specific aquifer a well or well field is taking water from. It can also lead to confusion regarding whether multiple wells are taking water from the same aquifer.[1]
[1] Hazen Russell, Natalia Baranova, Marc Hinton and David Sharpe, "Consolidating the Value of Ontario Drinking Water Source Protection: Data Mining for Well and Aquifer Information," paper prepared for GeoOttawa 2017. See section 4.3.