Sources of water
Most of the water on Earth is in oceans and seas; it is salty and not fit to drink, because salt dehydrates the body. Fresh water is scarce, and most of it is stored in glaciers, especially in Antarctica; the rest is in rivers, lakes, swamps and groundwater. People have long lived beside rivers and lakes. River water changes with the seasons: in spring melting snow causes floods, in summer some rivers become shallow. So reservoirs are built: a dam blocks the river bed and creates an artificial lake. A reservoir prevents floods, stores water for irrigation and drinking, and a hydroelectric station at the dam works: falling water turns a turbine and electricity is produced. Dams also affect nature: they block fish routes and reduce water downstream. Pieces broken off glaciers — icebergs — float into the ocean; most of an iceberg is underwater and only a small part shows.
“Water map”: on a globe or map find four oceans (Pacific, Atlantic, Indian, Arctic), three seas, two lakes and two rivers and write them down. Mark each fresh or salt.