Crucial to our existence, water sustains all life on Earth. Following the old adage, "What goes around comes around," water moves continuously through the stages of the hydrologic cycle (evaporation, condensation, and precipitation). How does our drinking water fit into this hydrologic cycle? Where did the water we drink fall as precipitation? Did this water percolate down into the ground as part of a groundwater system, or did it remain on the surface as part of a surface water system? What path did this water follow in order to become our drinking water? This lesson will explore the hydrologic cycle and water's journey to our glass.
Conduct a large-group brainstorming session on the various places where liquid water can be found on Earth. Create a list of places, such as oceans, lakes, rivers, aquifers.
Show students a glass of water. Unless the water came from a rain barrel outside the door, this water probably traveled a great distance to end up in that glass. Challenge students to learn the path the water traveled.
Help students identify the drinking water source. Is the drinking water from a well or from a public water supply? The home water source may be different from the school's. Use terms such as "aquifer" and "reservoir" to describe where water may be found.
How did your drinking water get to this source? Using a map and information from the United States Geological Survey water division or your local water office, trace the path of your drinking water. Encourage students to describe the areas where precipitation falls and how it moves to other places. (Gravity plays a major role.) Boundaries or drainage basins can be identified. Students should note the different places the water in the glass may have traveled and write these in their journals or on paper.
Example: In Topeka, Kansas, the public water supply is drawn directly from the Kansas River. The water follows this path to get there:
Working from the immediate source of your drinking water (a reservoir, for instance), follow rivers and streams on the map back to their headwaters. Older students may want to work in groups for this. Be sure to discuss the choices in deciding if nearby streams actually flow to the same point. Look out for elevation changes that might send a stream flowing in another direction! Note the size and names of the water conduits (e.g., rivers, lakes, streams, brooks, or creeks). End by having a map with highlighted boundaries that define the drainage basin or "watershed" from which your drinking water comes. Rain or snow that falls within the boundaries might wind up in your drinking glass or water fountain; precipitation that falls outside the boundaries flows someplace else.
Have a brief class discussion. What have students learned about water that they did not know before?
Have students sketch a map in their journals or on paper, showing the path of their drinking water from the point of precipitation to where it is drawn as drinking water.
The final sketches should show some extent of boundary, several water features (possibly surface and subsurface), and the direct source for tap water. Students should understand that this movement of water is just part of the greater hydrologic cycle.
Where does water travel beyond your town? Trace water's journey on a map from your location to where it eventually will evaporate, sink below the ground, or enter an ocean or a lake with no surface drainage (such as Utah's Great Salt Lake).
Make a watershed model demonstrating how water drains.
About.com: Water and Hydrology
EPA Watershed Information Network
Environmental Literacy Council