摘要
Water is essential to all living organisms.From humans to plants and animals to bacteria,everything on Earth needs water to survive.About 71%of the planet's surface area is covered in water,and when seen from space,the Earth looks blue.That is why it is called the“blue planet”.Approximately 98%of all water on Earth is salt water,which is found in oceans and seas and is home to hundreds of thousands of marine species.Only about 2%is fresh water-the water we depend on.
