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UNIT 8: WATER in, WATER out(plumbing) INTRODUCTION We need clean water to drink, wash, and cook. And we need to take dirty water away. The system of pipes that does this is called plumbing. It is a very important part of any building. STORY 1: The Water Supply System Clean, fresh water comes into the building through pipes. This is the water supply system. The water comes from the city main pipe under the street. A pipe connects your building to this main. Inside the building, the pipes go up to