Re: What is water pressure and how does it change at different depths?

Hello Nibras!

As you have already learned, water pressure increases as depth increases.      
Pressure by definition is force over unit area (force divided by area).
A good example is pounds per square inch or "psi".

In order to reinforce your system conversion skills, I will present the
information in English units and you can convert to SI if that is 
necessary.

The pressure of water increases by 1 psi for every 2.313 feet of depth. So
the pressure 100 feet deep in the ocean would be 

                100 ft/2.313 ft/psi  = 43.24 psi + 1 atmosphere (about 14.7 psi)
                                     = 57.9 psi

This relationship also works for holding tanks like water towers.  For
example, say you have a cylindrical water tower 70 feet tall and you would
like to know what the pressure is at the bottom. 

                70 feet/2.313 ft/psi = 30.26 psi + 1 atmosphere (about 14.7 psi)

This means that each square inch of surface area on the bottom of the tank
is being pushed downward with a force of 44.96 pounds.

The height of the water is called the water column and the diameter of the
water column does not matter. the pressure at the bottom of the 70 foot
tower would be 30.26 psi whether the tower was 100 feet in diameter or 1
inch in diameter.

The point is that as you go deeper into a fluid, or the taller the water
tower, pressure increases, and you go toward the surface or lower the level
of the water in the tower, the pressure decreases

Basically the pressure at the bottom of the tank in psi is the same as the
weight of the water supported by each square inch of the bottom surface of
the tank.

You also asked for reasons why this can be important.  A big reason is
maintaining the system pressure in city water lines.  All the water towers
you see along around the cities and towns are there to maintain water
pressure in the city water system so that water flows when you open a tap
in your house. 

Here is a web site that you might want to look at to learn more:
 http://www.challengers101.com/Pressure.html

I hope this is helpful for you.  Good luck with your project.
Greg

[note added by MadSci Admin:  It is very fortunate for you that our answering
scientist was extremely prompt in returning his answer.  If the answer had
taken the usual 7 to 10 days to be returned you would not have received this
answer in the time limit you allowed.  The take-home message to you is that
you need to not wait until the very last moment to work on projects or reports.
In future you may not be as fortunate if you wait to the end.]