Sources of well water

Wells

There are over 50,000 private wells in the Ottawa area. Well owners are responsible for ensuring that water from their wells is safe to drink, and that their wells are not contaminating the groundwater. Wells must be properly designed and maintained to ensure that drinking water is safe.

Common types of wells: Dug and bored wells (with casings 60 to 120 cm/24 to 48 in.) are less expensive to install than drilled wells. Like sand point wells, dug/bored wells are prone to near-surface contamination and shortages. Drilled wells (casings 10 to 20 cm/4 to 8 in.) cost more but penetrate deeper aquifers.

Cross cut image of a dug well

Cross cut image of a dug well

Cross cut image of a drilled well

Cross cut image of a drilled well

Where water comes from

The water we drink generally comes from surface water (above ground) or groundwater (underground). Only about 1% of the Earth's water is surface and groundwater.

The water cycle: Rain or melting snow can take several paths. It can runoff into streams, lakes or rivers. It can seep into the ground to be used directly by plants or to recharge groundwater. It can evaporate and return to the atmosphere. The cycle is complete when water in the atmosphere returns to earth as rain or snow. Groundwater from a deep well may have been in the ground for hundreds or thousands of years. In a shallow aquifer, the water may be a few weeks or years old.

The hydrologic cycle

The Hydrologic Cycle showing how rain or snow runoff pools underground to provide water

The Hydrologic Cycle showing how rain or snow runoff pools underground to provide water

How water moves

Groundwater flows from areas of higher elevation and/or pressure to lower elevation and/or pressure. It can flow horizontally or vertically upward or downward but usually in just one direction. This direction of natural flow can be affected or changed by pumping a well. How fast groundwater moves depends on how porous the soil or rock is, and whether the groundwater surface is sloped. The speed of water movement varies greatly.

The water table: The point at which the ground is saturated determines the water table. This level rises and falls depending on rainfall and local water use. Taking water out of the ground faster than it is recharged by the water cycle will lower the local water table.

Contamination

Is it clean? When an aquifer gets contaminated, the water may be unfit and unsafe to use. Groundwater can become contaminated in several ways:

  • spills on the ground, e.g., fuel and pesticide spills
  • injection into the ground, e.g., septic leaching beds, disposal of waste in wells, contaminated surface water running into poorly constructed or maintained wells
  • improper handling of industrial solvents and chemicals
  • waste leakage, e.g., manure storage, wastewater, septic tanks and landfills
  • leaking underground and above-ground fuel storage tanks
  • groundwater travelling from contaminated to clean aquifers
  • over-application of manure, commercial fertilizers or pesticides

Whether the groundwater gets contaminated depends on:

  • the size or strength of the contamination source
  • the ease with which the contaminant can move into or travel through the soil
  • out how to protect your well from contamination.