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the big picturethe water cycleThe water cycle is an essential backdropto all life. It nourishes the land, sustains flora and fauna,allows food to grow and carries away wastes …Would it surprise you to discoverthat the ice in your glass oflemonade was once a snowflake?How about if the tears in your eyes,were, long ago, drops in a poolwhere dinosaurs came to drink?Well, both are possible. Nearly allof the water on Earth is the samewater that has been here sinceour oceans formed nearly fourbillion years ago. Each raindropand snowflake that falls is on anendless path from the sky to theground (or ocean) and back to thesky again. This loop is called thehydrologic cycle, or water cycle.Each drop of water takes a uniquepath on its quest. For instance, ifa drop falls into a river it mightstay there for three weeks. Ifit touches down in a glacier, itcould remain frozen for hundredsof years. If it sinks into thesoil, the drop could be trappedunderground for as long as fortythousand years. Eventually,though, all water that falls findsits way back up into the air tokeep the cycle going.T Strain Trueit, The water cycle, Franklin Watts,USA, 2002, pp. 7–8.We can’t create new water – we can only usewhat already exists. Day after day, year afteryear, millennium after millennium, MotherNature has moved vast quantities of wateraround the planet. This movement of wateris the essential backdrop to all life, includinghuman existence. However, we humans tendto notice only the more obvious signs of thisongoing exchange, such as clouds and rain.This is an awe-inspiring cycle. Chances are,however, that you learned little about it inyour school days, or if you did, you may bea bit rusty on it! It’s worth remindingourselves of its fundamentals.All life functions against the backdrop ofa continuous water cycle. The evaporationof water is the central feature of this cycle.Without evaporation there would be no rain.Water is continuously evaporating from allsurfaces – from oceans, rivers and lakes, andfrom the land, vegetation and every breaththat every animal expires. This evaporated waterpasses into the atmosphere and forms moisturein the cooler layers of air. The moisture gathersto form clouds which are carried around theEarth by wind currents.Under the right conditions these clouds releasetheir moisture as rain, hail or snow. When thisfalls onto the land, much of it seeps into thesoil. Some of it is taken up again by vegetation,some filters down into underground aquifersand the surplus flows as surface water intorivers, lakes and streams.The seemingly endless quality of this cycleis deceptive. Superficially, it looks as thoughthe supply of fresh water should be abundant.The reality is very different, however. Risingaverage temperatures mean that, in manyplaces, less water vapour forms into rain.At the same time, the burgeoning globalpopulation is placing ever-increasing demandson the planet’s reserves of fresh water.12 Victorian Women’s Trust - Our Water Mark