It sounds simple although we would suggest that you call us on 01189736905 before you buy any long lengths of water or hose pipe. The information that we will need will be the flow rate at the water source, for example the tap of pump outlet. The length of pipe or hose pipe that you would like to run. The water pressure at the source if available. What you intend to use at the end of the pipe.
Our advice is simple call us with the information above and we will tell you which pipe diameter you should buy.
If you are buying a hose for the garden and it is less than 50 metres in length then you should be fine buying a standard 12mm hose pipe.