WATER Do you have a reusable water bottle in your backpack that you fill at home or at school Beyond the tap and water fountain where does that water begin Where does it end The Water Cycle It may seem that when it rains water comes from an endless supply in space But rain is part of the water cycle here on Earth The water cycle also called the hydrologic cycle recycles the same water over and over 1 Evaporation The sun provides heat energy The sun evaporates water from the oceans lakes rivers and streams It becomes water vapor 2 Transpiration Water also evaporates from the leaves of plants 3 Condensation Water vapor rises into the atmosphere where the air is colder There the water vapor condenses into clouds 4 Precipitation Air currents move clouds around the Earth Water droplets form inside clouds Droplets fall to Earth as rain and snow precipitation 5 Collection Rain melted ice and snow flow into the ground and waterways Water older than the sun Scientists think water may be even older than the sun Why They have tested water for clues The formula for water is H2O which means two hydrogen atoms are bonded to one oxygen atom But some water molecules also contain an extra molecule called deuterium Deuterium water exists on other planets and moons and in small parts on Earth How did it get here Scientists think it may have traveled in a giant cloud across the solar system before the sun began to burn 4.6 billion years ago Tastes pretty fresh for water that’s billions of years old doesn’t it 8
Where on Earth Is Our Water Fresh water 79 frozen in ice caps and glaciers 20 groundwater 1 surface water Earth’s water Salt water 97 Fresh water 3 Only 3 percent of Earth’s total water is fresh water We need fresh water for drinking Most drinking water is tap water and it comes from surface water or groundwater Rivers lakes and reservoirs are surface water easily accessible to us Water pumped from wells drilled into aquifers is groundwater What’s an aquifer Picture a dog at the beach digging a hole in the sand If the dog digs deep enough it will hit water This water comes from an aquifer a layer of rock that water can seep through The groundwater comes to the surface either naturally as in a spring or by being pumped up to the surface as in a well The not-great news Reverse osmosis requires a lot of The salty sludge left over could affect delicate ecosystems in the ocean or ground like if you poured a pile of salt into your soup it just wouldn’t taste right Don’t Drink the Salt Water If 97 percent of our water comes from oceans and seas it makes sense to investigate drinking that water Ocean water is saline though which means it has a high concentration of salt in it Drinking it would make us sick energy Desalination is the process of removing salt from water For years people boiled the salt from water using evaporation or distillation Now water is forced through cartridges that trap the salt in a process called reverse osmosis 9 The better news In nature rain falls to the ground collecting and dissolving minerals The heat energy of the sun evaporates the water and leaves the salt behind Scientists are working on desalination systems that use solar panels to copy nature’s own process
From Source to Tap to You 1 Surface water and groundwater move along a network of pipes to the filtration plant 2 At the plant water passes through screens and sand and gravel filters to remove contaminants and bacteria Chlorine kills potentially harmful organisms Then the water is aerated to release gas and remove the rotten egg smell 3 Pipes connect to your home or school via the underground system Turn on the tap Voilà water 3000 2000 BCE The Indus modern-day Pakistanis use terracotta pipes to get human waste out of homes 2000 BCE Wealthy Egyptians use a sand-filled container as their toilet 200 BCE A Western Han Dynasty tomb in China features a stone toilet seat 500 1500 CE In the Middle Ages people used chamber pots and threw the contents out the window 1596 Sir John Harrington invents the flushing toilet for his godmother Queen Elizabeth I 10
to Down the Drain What happens to water that goes down the drain It gets a new name wastewater The wastewater journey is like the tap-water trip in reverse TREATMENT PLANT 4 Toilets tubs showers and sinks drain into pipes that lead to the sewer system under your street They send the water to the wastewater treatment plant 8 The final wastewater pushes through sand and charcoal filters and then is sent to a nearby waterway and the cycle begins again 5 Screens filter out anything that’s not pee poo or toilet paper Leftover solids sink to the bottom of the grit tank and get sent to a landfill 6 The wastewater left over is filtered by gravity into sludge the heavy material water and scum the stuff on top Sludge and scum go to a digester a giant tank where bacteria eat and grow Some becomes fertilizer Some goes to the landfill 7 Water from the settling tank goes to the clarifier where chlorine and other chemicals kill remaining bacteria Wells and Septic Systems Many homes in rural communities use wells to get their water directly from underground and septic systems to dispose of wastewater Some wells are dug and others are drilled Wells can be 9 m 30 ft to 600 m 2000 ft deep depending on the aquifer Well water is tested to make sure it’s free from bacteria and chemicals When a well goes dry it can take thousands of years to restore the water Septic systems use a tank made of concrete or steel buried in the ground Wastewater flows through the tank into a drain field where pipes with holes are buried in gravel The ground absorbs the wastewater Never place a well too close to a septic system or vice versa Q What’s the difference between gray water and black water A Gray water is drained from sinks showers bathtubs and washing machines Some people reuse gray water in their gardens Black water comes from toilets You wave black water goodbye when you flush but scientists are working on recycling it 1850 Earth closets are used Pull a lever and clay covers the contents of the pan 1890 Toilet paper rolls are invented gratitude 1910 The modern toilet with a closed tank starts to be used 1992 Low-flush toilets become available Using one saves 49 000 L 13 000 gal of water per year Today At least 2 5 billion people don’t have access to sanitary toilets And many don’t have toilet paper Tomorrow Scientists are creating a toilet that recycles wastewater into drinking water Yes it’s true 11
