How can one broken pipe cause trouble all over town?

Think of the last time you turned on a tap. Cool water rushed out and splashed over your fingers. Across town, other children were washing their hands at that same moment.

Now picture one pipe cracking under one street. Soon, people far away have trouble with their water too. How can one broken pipe cause trouble all over town?

Under the road lies a big pipe called a water main, the large pipe that feeds many homes. Smaller pipes branch off it into each house, like twigs off one branch. Because all those homes share the water main, whatever happens inside it reaches every one of them.

Inside the pipes, the water presses hard against the walls and keeps pushing forward. That push is called pressure, the squeeze that sends water up and out of your tap. Pressure is the reason water can climb all the way to a top floor bathroom.

Now the water main cracks. Water bursts out of the hole, bubbling up through the road and flooding the street. Water rushes toward the easy way out, so much less of it carries on down the pipe.

With water pouring away, the pressure drops in every pipe joined to that water main. Homes streets away turn on their taps and get a weak trickle. Houses high on a hill get no water at all.

Water workers from the town hurry over to mend the crack. They cannot fix a pipe while water is gushing out of it. How do you think they could stop the water?

Along the water main sit valves, metal gates that workers turn to open or close the pipe. The workers turn the valves shut on both sides of the crack. Now the water stops at the gates, and the workers can reach the hole.

A shut valve stops the water for every home past it, not only at the crack. That is why whole streets, a school and shops lose their water while the workers mend the pipe. One crack, and lots of neighbours wait beside dry taps.

One broken water main lets water escape, so the pressure drops in every pipe joined to it. Then workers shut the valves to fix it, and every home past those valves loses its water too.

Under all the busy streets, the pipes spread out like the branches of one great tree. Houses, schools and shops hang from those branches like leaves. When one big branch cracks, every leaf along it goes thirsty.