We've made a water-supply unit by punching a hole near the bottom of a one-quart milk carton, and inserting the end of a one-yard length of rubber tubing into the hole. It fits snugly because we sealed it with an O-ring. For our purpose, the tubing is a water pipe.

We found a cut-off valve on the clothesline! For the students whose families have dryers, we will explain that this tool is made of two small pieces of wood, and has a
metal spring holding them together. When we pinch the open ends of the tool together, the closed end opens. It is made to attach cloth to a small rope, usually outside, so that the cloth items (our clothes) can dry in the fresh air and sunshine. It is called a "clothespin."

As you can see, this tool is good for many things. In this case, it will be good for closing the pipe when we do not want the water to run through the pipe. Real pipes have
shut-off valves that look like water faucets. They ARE water faucets!

We will close the pipe by clamping the shut-off valve onto it, and fill the water tank (milk carton) with water.

Gather around the reservoir (wash-pan or empty aquarium), and watch what happens. It is important to remember that many city water supplies include a reservoir up on a hill, or a tank that is built on top of a tower. Both water-supply units have pipe leading out so that water can flow into the water mains (great big pipes) that supply water to the city (or a part of the city).

Many farms have wells that pump water up into an elevated tank, where it is held until it is needed. When it is needed, the shut-off valve is turned so that water can flow
through the pipe.

We know that gravity pulls the water down. Do we know what controls the water that is pulled down by gravity?

One control is the height of the reservoir or tank. We can see this by holding the milk carton up high, and watch how fast the water flows out through the pipe. By holding it closer to the container into which we are guiding it, we can see that it does not flow as fast. That means that if the water flows fast, the container gets more water in a short period of time. If it flows slowly, it takes longer to fill it.

The other control is the valve. If we want to fill the sink or bathtub at home, we turn the faucet on all the way, and the water comes out fast. If we just want a little bit of water, we just turn the faucet a little way.

Another control is the size of the pipe. More water can flow through a fat pipe than through a skinny pipe. That is probably the reason that fire hoses are fatter than garden hoses. It takes lots of water, in a hurry, to put out a fire; it only takes a little bit of water, sprinkled on gently, to water the flowers.

We have two controls here in our experiment: we can hold the carton high or low to make more or less water come out of the tube; and we can clamp off part of the tube, with the clothespin, to make the pipe more skinny, or take it all the way off, to use up all the space of the tube.

We have seen how nature's force (gravity) has been combined with man's intelligence (tools) to bring water to places where it is needed. This is how some kinds of irrigation systems function.

It was the knowledge of bringing water to places where it is needed that the State of Israel was able to "turn a desert into a garden."