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
GROUND LEVEL WATER TABLE Figure 1 3 Since older wells were dug by hand they were made about 3 feet 1 m in diameter just big enough for a man to stand in the hole while digging it These early wells were lined with stone to keep earth from falling into the hole The Indus Valley in present day Pakistan had this type of well 5 000 years ago Later civilizations used clay bricks to line their wells Fig ure 1 4 Today wells are dug by machine and are no bigger than the 2 to 4 inch 50 to 100 mm diame ter steel pipe that is drilled into the ground Since modern drills can go through rock as well as soil wells can recover water that flows through cracks in the rock hundreds of feet below the surface WHAT IS HARD WATER Sometimes as water passes through the earth it picks up salts of calcium and magnesium You can identify hard water by boiling it in a pot and noticing that a white crusty residue forms on the inside of the
W wler LIU W IU ROUND LEVEL WATER TABLE UAW Figure 1 4 The type of earth or rock through which under ground water flows limits the amount of water that flows into a well To supply water to larger families and villages larger and deeper wells were needed Such town wells can still be seen in the central squares of many old villages in Europe and Asia Many towns today rely on wells for their water supply But these wells reach down past several lay ers of soil sand and gravel into what is called an aquifer or layer of porous water holding rock These aquifers were originally pure but as people used fer tilizers and chemicals on their land the chemicals began to seep down into the aquifers Thousands of wells all over the world are now too polluted to drink from Only the deepest aquifers remain unpolluted today THE FIRST AQUEDUCT Fourteen hundred years ago the Greek engineer Eupali nus of Megara was given the task of supplying water to the city of Samos To accomplish this he built one of
