Erie County
Water Authority
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Water Cycle / Hydrologic Cycle

Water travels through the air to become part of a cloud - this is called evaporation. It falls to the earth as precipitation, such as rain or snow, and evaporates again. This is repeated in a cycle - just like the wheels that turn on your bike, but without brakes. The Hydrologic Cycle never stops. If the hydrologic cycle stopped, no life on earth would survive. Plants would die, rivers, lakes and oceans would overflow and flood the land and our entire ecosystem would come to an end.

Precipitation creates surface runoff, which makes its way over the earth to fill the lakes and rivers. Percolation is the way water moves through the soil into the earth to replenish underground aquifers. Places close to the oceans or lakes have more precipitation because there is more evaporation to form clouds. Clouds travel over mountains and the vapor condenses to form precipitation and freezes. That is why you see snow caps on mountains.


  • Evaporation - liquid water becoming a gas
  • Water Vapor - water as gas in the air
  • Condensation - water vapor becoming a liquid
  • Surface Runoff - water that runs along the soil and goes into lakes and rivers
  • Precipitation - rain, snow, sleet or hail
  • Groundwater - water under the ground, as in a spring or well
  • Aquifer - a large water source under the ground
  • Percolation - water moving downward through openings in the soil

Vocabulary Examples:

These terms are an everyday part of your life. Picture this:

When a glass of ice water "sweats" because the outside of the glass is warm and the inside is cold, the droplets that form are called condensation.

When mom or dad make coffee, water drips through the grounds into the pot, it's called percolation. This is the same way that water moves through the soil and into the aquifers underground.

When boiling water for macaroni, you'll see a "smoke-like" steam coming from the pot. This is one form of evaporation. It's water's gaseous state.

Did you ever notice when water drips off your hair when taking a bath? Water that is not soaked in by your hair runs off into the tub - this is called surface runoff. In this case, the water goes from the ground to another storage area - the sea or lake.

Learning Center Treatment Process Water Cycle
Story of Drinking Water Conservation and Storage Water Use