The proceture as shown below

1- Calculate the total flow rate according to number of fixture , type of application or numder of population ( See www.PDH on line.org )

2- Sellect recomended velosity according to your application there are tables for this purpose .

3- Inter charts ( as pipe material ) you have flow rate ( item 1 ) & velosity ( item 2 )

you can find pipe diameter & friction loss per length of pipe .

4- From tables calculate equivalent length for fittings , accessories & valves

5- Messure total lenth of the pipe + equivalent length for fittings ( item 4 ) =total equivalent length of network.

6-Find total pressure drop = friction loss per length * total equivalent length

7 - Pump head = ( total pressure drop + static head )*1.1 ( safty factor ).

8- From characrisic curve of pump manufacturer & pump type you need can be sellecte the pump for maximum effeciency .