The purpose of this paper is to develop a computer program to assist in the design of plumbing and sanitary system in consu1tancy services. An attempt v,;as made to lay the foundation for a reliable and efficient 'package type'. Program that will be able to handle the usual design challenges that are encountered in designing plumbing system in commercial and industrial application. A Visual Basic program are use to perform hydraulic calculation, water demand calculation, total pump capacity, pump horse power ana discharge unit calculation for plumbing system with pipes already diameter and layout pattern already known. The interactive program determine the flow rate in all the pipes, loading, and head losses in the pipes. The algorithm uses an interactive method of calculation and employs the Hazen William equation for frictional loss computation in the pipe. These project will assists consultancy field especially in plumbing system either to get the result of calculation or information about the system. There is the wide scope in plumbing system, there is cold water plumbing system include hydraulic calculation, sanitary plumbing, water demand and pumping system. A visual basic will be used to create interface with related toolbar and coding to complete software development.