Pumping capacity

For pumping water through 2" PVC pipe for gardening purpose up to a length of 1000 meters, what is the capacity of Motor HP required?

We are a housing society spread over 6 acres. We use a 5 HP motor pump to supply water from underground tank through 2" PVC pipe over a length of 1000 meters. We are not getting sufficient pressure of water even after 500 meters. Is the motor capacity insufficient?