Watering help again..........sorry

Sparkyaj. I have read every single post on the Vine since it started and don't remember a post showing how to calculate water pressure. Having worked for Welsh Water it would have struck a cord.
The water industry uses something called "meters head"; plumbers however deal in a term called "Barr".
I used to deal with telephone calls relating to water bursts and lack of supply. I would log the information and call the emergency engineers out.
Pressure normally relies on gravity to distribute the water, here in Wales. All our lakes and reservoirs tend to be up mountains. Well we do have rather a lot of them and that does tend to be where most of our rain, falls.
However in some parts of the country pumping stations are required. The water pressure is determined by how many meters water will shoot up into the air from ground level before it forms a mushroom like umbrella and falls back to earth. If water goes up five meters before falling back to earth then it is described as having pressure of "five meters head" not very scientific but that is how they calculate the information.
Anyway I am waffling and not helping so I will have to leave it to a better person to explain. hopefully someone will know. and be able to help?
Jax

Oh, thanks for the info. ALl I was trying to establish is if I would get enough water pressurefrom a tiny header tank say 15ft in the air and then pump my large supply upto it when I need the irrigation system.

In full I thought,

Large tank at back of garage with gutters and tub diverted into it. take a pumped supply upto a header tank on the roof of the garage and then run supply down to a tap.

I thought I could put a timeclock onto the pump supplying the header and then leave the taps to the irrigation turned on.

that way, I can program the header via the pump to do all of my watering without going out each night.