How the Local Groundwater Data Is Calculated

The datasets

Well records

• What is counted. Every record in the Water Well Information System located inside the municipal boundary, of all types: water supply wells, test holes, monitoring and dewatering wells, and abandonment records. Locations and values are as submitted by well contractors, and MECP notes that inaccuracies exist.
• Median depth of wells with a water level, and median static water level. Both medians are taken from the same records: those inside the boundary that report a depth greater than zero and a static water level at or below ground (flowing wells, recorded as above ground, are left out). Using one set of records means the two figures describe the same wells, so the median water level cannot come out deeper than the median depth simply because different records were counted. The panel shows how many records the medians are based on, and pages call the first figure the median depth of wells with a water level for that reason.
• Records reaching bedrock. A record reaches bedrock when its depth to bedrock is reported and its total depth is greater than that. Where depth to bedrock is blank, a bedrock layer in the formation log of the county Well Record Data Report counts. The share is of all records with a depth, a larger set than the one behind the medians, because many records report a depth but no water level. Where a page gives both figures, it says which set each comes from.
• Supply and monitoring shares. Where pages quote them, these come from the first code in the WELL USE column of the county reports: domestic, livestock, irrigation, commercial, public, industrial, municipal and cooling uses count as supply; monitoring, test hole and dewatering codes count as monitoring, test or dewatering wells. The share is of records with a stated use.

Permits to Take Water

• Active permits. Permits flagged as active in the ministry dataset with a source located inside the municipal boundary. A permit with several sources is counted once.
• Purpose categories. Permits are grouped by the dataset's purpose category field. That field uses two names for farming: an older ministry category, Agricultural, and a newer industry-sector name, Agriculture, forestry, fishing and hunting. Panels and page text count farm uses together as one group, "Farm uses", with the split in brackets, for example "Farm uses 21 (13 + 8)": the first number is the Agricultural label and the second the farm uses under the newer label. Where one of the two is zero, only the total is shown, for example "Farm uses 7". Farm uses are crops, nursery and sod, orchards and livestock. Every permit under the older Agricultural label is a farm use. Under the newer label, a permit joins the group only if its specific purpose is a farm use (field crop, covered crop, nursery or floriculture, sod farm, fruit and tree nuts, animal production); others, such as aquaculture, food processing or "other", are shown as "Agriculture, forestry, fishing and hunting (non-farm or unspecified)". Every other category is shown under its own label as published, and the underlying data files keep the labels separate. Panels list the three largest groups; where two have the same count, they are ordered alphabetically by label.
• Construction and dewatering permits. Permits whose purpose category is Construction or Dewatering Construction, or whose specific purpose names construction, road building or general dewatering. Pits and quarries are not included.
• What is missing. Construction dewatering registered on the Environmental Activity and Sector Registry is not in this dataset, so in cities the permit count understates how much construction dewatering happens.

Conservation authorities and provincial plan areas

Shares of a municipality's area are calculated from a grid of sample points about 500 m apart inside the municipal boundary. A conservation authority is listed when it covers at least 1% of those points. The Oak Ridges Moraine, Greenbelt and Niagara Escarpment Plan shares use the same grid. Wellhead protection areas are not available as an open province-wide dataset, so they are never shown as a data value; pages describe them from the source protection documents they cite.

What the figures cannot tell you

Medians describe the records in a municipality, not the ground under one property. Older wells, shallow dug wells and private wells built before reporting was required are under-represented, and record locations can be approximate. A hydrogeological study measures the site itself: boreholes, monitoring wells, water levels over time and testing. Use the panel to understand the setting, not to replace site data.

How the figures are kept current

The datasets are re-downloaded and the figures recalculated in a quarterly refresh. Numbers in the page text are drawn from the same data files as the panels, and an automated check fails the site build if a figure in the text no longer matches the data.