The Sustainable Water Well Infrastructure (SWWI) Expert Panel Report: 'Water Well Sustainability in Ontario' [pdf] : Ontario has two principal geologic materials, which can be tapped for groundwater supply: fractured bedrock and sand and/or gravel overburden deposits. Bedrock is found throughout the Province and is the result of several billion years of geologic activity. The sand and gravel deposits, which are less than 100,000 years old, are associated with advances and recessions of continental ice sheets that covered the Province. Together, these two geologic formations form aquifers which provide storage for groundwater resources and a perpetual water supply to wells... Adequate groundwater for domestic supplies of up to 5 m3 /day can usually be obtained by drilling wells a few tens of metres into most of the bedrock or overburden materials found in Ontario...
The Dundee and Detroit River aquifers are also found in the southwest corner of the Province (south of Lake St. Clair), but the water is often sulphurous. As a result, it is mainly used for irrigation purposes. The mineralization in this area increases with depth. The region between London, Sarnia and the north shore of Lake Erie is underlain by shales. These formations yield small supplies and the water quality is usually poor.
Once I realized that I should be searching for the word, 'aquifer' as opposed to 'groundwater table' or 'water well essex windsor', I was finally able to find information on the topic:
Analysis of Agricultural Water Supply Issues (pdf) : The Southwestern Area has two major bedrock aquifers -- the Dundee Formation and the Detroit River Group (Lucas and Amherstburg Formations). The Detroit River Group has the highest permeability of the two but both are widely exploited for domestic, municipal and industrial uses... The upper portions of the Detroit River Group is used as a plentiful irrigation supply south of Lake St. Clair. The supply however, can be sulphurous in places.
This has been the hardest question so far. The closest information I can get to "right here" is the proposed second span of the Ambassador Bridge:
Ambassador Bridge Replacement Span – Environmental Presentation:
* Four Distinct Aquifers:
- Water Table aquifer – essentially non-existent
- Overburden aquifer – within 4 meters of surface regionally, near surface in site study area, has generated artesian conditions
- Contact aquifer – located at bedrock/overburden contact zone, largest aquifer with respect to area
- Bedrock aquifer – located within the bedrock, has generated artesian conditions
Again, my profound lack of understanding of the geology and geography of where I live, has humbled me greatly.