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Well Water Safety

Basic Groundwater Principles


Hydrology is the science of water occurrence, movement and transport. Hydrogeology is the part of hydrology that deals with the occurrence, movement and quality of water beneath the earth's surface.

Water is continually moving within and above the earth in a cycle known as the hydrologic cycle or water cycle. This cycle ensures continual recycling of water throughout the environment by receiving energy from the sun. There are six major components of this cycle:

Basic Groundwater Diagram


  • The combined effect of evaporation and transpiration


  • The process of returning moisture back to the atmosphere.
  • Water (e.g. river, lake, etc.) is warmed by the sun's heat until it reaches the point at which water turns into the vapour or gaseous form.
  • The water vapour then rises into the atmosphere.


  • The process by which plants return moisture to the air.
  • Plants take up water through their roots and then lose some of the water through pores in their leaves.
  • As hot air passes over the surface of the leaves, the moisture absorbs the heat and evaporates into the air.


  • The cooling of water vapour until it becomes a liquid.
  • As the dew point is reached, water vapour forms tiny visible water droplets.
  • When these droplets form in the sky and other atmospheric conditions are present, clouds will form.
  • As the droplets collide, they merge and form larger droplets and eventually, precipitation will occur.


  • Moisture that falls from the atmosphere in the form of rain, snow, sleet or hail.
  • The amount, intensity and form of precipitation will impact whether water will infiltrate the ground.


  • The entry of water into the soil surface.
  • Infiltration helps to sustain the ground water supply to wells, springs and streams.


  • The downward movement of water through soil and rock.
  • Ground water percolates through the soil similar to water filling a sponge.


  • The movement of water over the earth's surface towards low lying areas, streams, rivers, lakes, etc.
  • The characteristics that affect the rate of runoff include rainfall duration and intensity as well as the ground's slope, soil type and ground cover.

How the hydrologic cycle relates to groundwater and your well

The hydrologic cycle consists of:

  • Inflows - adds water to the different parts of the system. For example, percolation of water into the ground recharges the aquifer (a saturated and permeable formation that can yield useful amounts of water for water supply).
  • Outflows - removes water from different parts of the system. For example, the discharge of groundwater from the aquifer to a stream or to a well.
  • Storage - the retention of water by parts of the system. For example, clouds and aquifer retain water for storage.

It is the continuous recharging of the aquifer that allows your well to receive a sufficient supply of water.

Diagram showing types of aquifers and pathways of recharge