Morris,

Junction numbers (or any id number) need not be sequential in epanet. We use ranges of numbers to identify different types of features. e.g. 1000's are junction nodes, 2,000's are wells, 3000's are water treatment plants and so on. The same approach can be used with pipes, pumps and valves.

I don't know if there are any memory or performance impacts of non-sequential (sparse) numbering schemes. If there are they haven't had any practical impact on us.

I understand that when Lew Rossman releases the next version you will be able to use alphanumeric symbols to represent features. That will make models a lot more "readable".

Regards,
Ben Harding
blh@hydrosphere.com