# Calculation of water pressure from a gravity fed irrigation system

I am planning a new tree nursery, and am exploring the gravity-fed water system options. There is room to place 2,146 trees in the area, they each require 2.5 gallons of water every day. I want to use 1 gallon per hour (gph) drip emitters and break the trees into 17 different zones with a maximum of 128 trees per zone. The drip irrigation requires 20 psi to work properly, and a reducer can be installed to keep the pressure from being too high. Assuming these are all on a level surface, what size tank would I need with what dimensions to keep the lines pressurized with a minimum of 20 psi after a daily 5,365 gallons have been applied?

I don't think the size of your container will affect the pressure of the water contained in it, as much as the depth of the water. If you want to have $$20 \; psi$$ and the entire system is on level ground, then you will need to have a container with the water level at a minimum of roughly $$46 ft$$ tall. $$Pressure (psi) = \frac{Volume}{\pi R^2}$$ where $$R$$ is the radius of your cylindrical container. That gets you the height. To convert that height to $$psi$$, just multiply the value by $$4.333$$. That's how I got the number $$46$$. So, in conclusion, you want to have your water source at $$46 \; ft$$ above where you want there to be $$20 \; psi$$ (Note that you don't need to have $$46 \; ft$$ of water, rather the water is just $$46 \; ft$$ above the system).