When you turn on the tap（水龙头）in your house, water comes out. This water has 1 a long way. This water comes from rain in the sky. The 2 that water arrives to the tap in your house is called the "water supply".

Most of the water on the earth is in the 3 . This water has a lot of salt in it. We cannot drink this water. Salt water makes us ill. But when the sun shines, it 4 a part of the ocean. This water rises up to make clouds in the sky. The more water rises up, the heavier and larger the clouds become. The clouds will get so heavy and large that they will change colour from white to 5 . The water will fall down into rivers and lakes 6 rain and travel back to the sea. This is called the "water cycle". We use half of the rain water 7 falls over the earth.

There are parts of the world where there is 8  fresh water. In the Arab countries, salt water can be made safe to drink. This is done by freezing or boiling it. The salt is left 9  and the clean water is then taken off. This process（过程）is very 10 , but in some areas this is the only way to get clean drinking water.