First, determine the pressure needed for your sprinkler or whatever. Then
determine the volume of water needed per minute. Then get a pump that
delivers the needed volume at the needed pressure. Do a search on "sprinkler
pump" for more info.
http://www.google.com/search?hl=en&l...sprinkler+pump

Bob

"Eugene Ferreira" wrote in message
...
Hi

I am trying to find out how you determine what sizeof pump you need to
keep
the water pressure in an irrigation system. I stay on a farm and we're
watering from a dam, so there is no water pressure.