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Water pressure and flow rate

The sketch at left shows a picnic cooler full of water. When you first open the spigot, the water flows out rapidly. As the water level drops, the flow slows down. Press the start button and watch this happen.

The weight of the water on top creates pressure on the water underneath, which makes it spurt out rapidly when the spigot is opened. The pressure is proportional to the depth of the water above the spigot. As the water level drops, there is less pressure, so the flow through the spigot slows down.

This explains why small towns have water towers. Water is stored up high in a tower, so that when you turn on the tap the pressure is strong enough to push the water through the pipes and out of your faucet at a reasonable flow rate.

Click here to see a water tower in action.

This applet was written by Lisa Denise Murphy at the University of Illinois. Early drafts were written in 1999. The current version was last revised in January of 2000. Permission is given for students and teachers to use this applet, provided acknowledgement is made of the source. Anyone interested in using this applet in connection with any published paper or commercial venture should please first consult the author. Thank you.

This page last revised January 19, 2000.