# Water pressure calculation for a volume of water at a given height

I'm looking to create a rain harvesting system. I have a 275 gallon IBC tote that is 48" x 40" x 46". I have an adapter for a 3/4 garden hose at the bottom of the IBC tote. I'm trying to figure out three things:

1. What is the pressure at the bottom of the tote, assuming that the tote is full?

2. Would the pressure from the column of water in the tote be able to reach an 8' tall planter 40' away via the hose?

3. How much would the pressure increase per foot that I elevated the tank?

• Volume doesn't matter. That is why you can dam a rising flood with sand bags regardless of the size of the body of water. Commented Jun 4, 2014 at 17:06

A. what is the pressure at the bottom of the tote, assuming that the tote is full.

Only the depth of the water matters.

$P=\rho gh$, where $\rho$ is the density of the water, $g$ is the acceleration due to gravity, and $h$ is the depth of the water.

B. would the pressure from the column of water in the tote be able to reach an 8' tall planter 40' away via the hose.

No, water will not rise about the height of the surface of the tote

How much would the pressure increase per foot that I elevated the tank?

$P=\rho gh$, where $h$ is the difference between the height of the surface of the water and the height of the point where the pressure is measure, such as the outlet of a hose coming from the tank.

• Roughly speaking, the coefficient is $\frac 12 \frac {psi}{foot}$ because one atmosphere ($14.7$ psi) will raise water $33$ feet. Commented Jun 4, 2014 at 17:07

In reviewing the answer supplied by troy, The explanation of his increased water pressure on the larger pipe is as follows:

The pressure from the tank is based on the height of the tank. A tank on a 25' tower will supply at least 12.5 pounds per square inch. (we don't know the height of the surface of the water.) The 3/4 inch pipe has an area of .44 sq in. Thus the 3/4" pipe will have a pressure of 5.5 psi. The 2" pipe has an area of 3.15 sq in. Thus it will have a pressure potential of approximately 40 psi. reducing the pipe down to 3/4" after the drop will increase pressure by about 2.6 so an estimate of the pressure on this pipe would be about 90 psi.

• I appreciate that you are adding to troy, but this isn't an independent answer by itself. Commented May 14, 2015 at 15:21

PSI does not change with pipe size, only the surface area it is pushing on. Static head pressure is .433 per vertical foot. Water cannot flow over the top of a vessel which is gravity fed. It will only flow as high as the water level in it, because the water in the hose is also pushing back with gravity. A lot of these answers you are reading are amazingly wrong.

Your pressures at each are identical, while the valve is closed. The real difference is the fact that 2" volume of water will easily supply two 3/4" outlets. While the other is diminished from loss due to physics. Its called friction loss, due to pipes, lengths, elbows, tees, etc.

When the pressure increases, the flow decreases thereby providing the same "power". You can have larger flow if you naturally decrease the pressure, or larger pressure if you restrict the flow.

• Welcome to Physics Stack Exchange. Feel free to look around to get an idea of how things work, and take the tour (under help at the top of the page). Now, this does not seem to answer the original question. Perhaps you could rework it to do so? Commented Jul 16, 2015 at 21:36

20 ft. of water has a static pressure of 8.66 because 20 ft. x 0.433 = 8.66

The static head pressure of 1 foot of water is 0.433

60 ft. of water is 60 x 0.433 = 25.98 pisg

• This is not a (complete) answer to the question.
– Danu
Commented Jan 3, 2016 at 12:28