gen If you look at a globe of Earth you will notice that the color blue predominates Blue is typically used to designate water which covers 71 percent of the globe This ocean water tastes salty and contains as many as 32 different salts and minerals If you were to drink it you would get sick Actually too much saltwater could easily kill you On the other hand if you were to put a fish from the ocean into fresh water it would swell up by a process called endosmosis and die Fortunately for us seawater is heated by the sun and evaporates leaving all the salts and minerals behind It then condenses into clouds that float around the sky and through precipitation release their water as rain or snow Figure 1 1 When rain or snow falls on the land it seeps into the ground and forms springs rivers and lakes that all eventually flow back into the ocean The water that we use comes from these springs rivers or lakes and is relatively pure This cycle of evaporation conden sation precipitation seepage and flow is the natural water cycle without which life on Earth would not be
a to I TT I EVAPORATION f RAIN RIVER OCEAN LAKE t FRESH GROUND WATER Figure 1 1 The First People Even the earliest humanlike creatures called Aus tralopithecines who lived 4 000 000 years ago knew how and where to find water When our human ancestors first left their cave dwellings more than 10 000 years ago at the end of the Ice Age or Pale olithic period they gathered in villages located near streams rivers or lakes They recognized that water was their most important commodity After all about 70 percent actually somewhere between 67 and 78 percent of the human body consists of water that must constantly be replaced Water in the body is used to help drive the digestive system to lubricate the body's joints to cushion the internal organs to cleanse the body both inside and out and to control the skin's temperature through evaporation as we perspire Our ancestors usually sited their dwellings close to water From their round huts of woven vines or
reeds covered with thatch these early people looked out onto a river or lake and drank its water washed in it and pulled out buckets of it to irrigate their gar dens Three thousand years ago on the banks of the Danube River and the lakes of Switzerland Stone Age civilizations of hunters and agriculturists built platforms on poles set into the river or lake bottom On these platforms they built clay floors with raised hearths They framed their houses with steep thatch roofs and triangular gables and walls of mud plaster or logs sharpened to fit into vertical grooved posts Figure 1 2 From these houses the people would lift buckets of water from the river or lake for their drinking and cooking needs They would also dump their waste down to the lake or river Isly are Ce Figure 1 2 At that time no one thought of separating the drinking water from that used for cleaning After all the lake was so large or the river so swift that one
person or even a family couldn't possibly become illfrom drinking the same water in which one washed WATER POLLUTION When water is polluted or contaminated it contains things besides oxygen and hydrogen Pour some water into a glass and look at its color Is it clear with no par ticles floating about Does it have an odor Polluted water often has the acrid smell of ammonia the same liquid that is used for cleaning Sometimes however polluted water looks perfectly clear because the offend ing bacteria are too small to be visible To be perfectly safe always have water from a new source tested in a laboratory before drinking it However the first families multiplied over time The village became a town and much later a city After a while the crystal clear lake or river gradually turned cloudy and people became ill from drinking its smelly water People noticed that water that flowed from a spring in the ground was usually clear So they began to dig wells in the ground as deep as necessary to find this clear water Figure 1 3 Water that flows into wells originates as rain or snow that seeps under ground through the earth which acts as a filter to remove dangerous
