A natural process called the water cycle links all the waters on our planet. Imagine the path of a raindrop ... it may fall on land or in the water. About one-third of the rain that falls on land flows straight into rivers and on to the sea. The other two-thirds soak into the soil. Some of the water in the sea eventually evaporates in the heat of the sun, and forms clouds in the sky. When the clouds are saturated with water, it rains. Thus, the raindrop completes its cycle.
One-third of the rain that falls on land flows into rivers and then the sea, but what about the other two-thirds that are absorbed by the soil? If we follow these drops, we find that they soak slowly down to a waterbed, at the rate of about one metre a year. The waterbed is also called a reservoir, or an aquifer. Water collects in these underground reservoirs over hundreds and thousands of years. Sometimes this information is written on the labels of mineral water bottles. Have a look!
Ocean water can be treated to make it drinkable. The process of removing the salt from seawater is called desalination. Unfortunately it is expensive, and consumes a huge amount of energy. About 65% of the water we use is pumped up from subterranean aquifers. All the water we use eventually drains into a river and flows to the sea, where the cycle of evaporation starts again. So the quantity of water on Earth remains the same. The amount of water on Earth today is the same as 100, 1 000 or 10 000 years ago. Just think, the water you are drinking may be the same water the dinosaurs drank millions of years ago!
When it is pumped up from the ground or drawn from rivers, water contains particles of dirt, bacteria and germs, which must be removed before it is fit to drink. There are several phases to the cleaning process. Let's look at water from the Seine, in Paris, and see how it is turned from a brown solution into drinkable water.
First phase The water is filtered to get the larger particles such as sand and leaves out.
Second phase The water passes through another filter with active charcoal to take out smaller particles and some of the microbial life.
Third phase The water is treated with ozone - a bit like having air blown through it. This treatment kills most of the microbiological 'pathogens' (extremely small particles that are invisible to the eye but carry illnesses).
Fourth phase The water passes through a micron filter, like a bunch of incredibly thin straws, to be perfectly purified.
Is mineral water cleaner than tap water? Tap water is safe nearly everywhere in the European Union, but many people prefer the taste of bottled mineral water to the taste of tap water. This is because water companies usually add chlorine to the water, to keep it clean as it travels over large distances to reach our houses.
출처: Environment for Young Europeans