The Design Of Potable Water Supply System For Institutional Setting
[A CASE STUDY OF KWARA STATE POLYTECHNIC PERMANENT SITE]

2.4.1 Pipes:  
Transmission or trunk mains usually convey large amounts of water over long distances such as from a treatment facility to a storage tank within the distribution system. Distribution mains are typically smaller in diameter than the transmission mains and generally follow the city streets. Service lines carry water from the distribution main to the building or property being served. Service lines can be of any size depending on how much water is required to serve a particular customer and are sized so that the utility’s design pressure is maintained at the customer’s property for the desired flows. Premise plumbing refers to the piping within a building or home that distributes water to the point of use. In premise plumbing the pipe diameters are usually comparatively small, leading to a greater surface-to-volume ratio than in other distribution system pipes. The three requirements for a pipe include its ability to deliver the quantity of water required, to resist all external and internal forces acting upon it, and to be durable and have a long life(Garg, 1994).
The materials commonly used to accomplish these goals today are ductile iron, pre-stressed concrete, polyvinyl chloride (PVC), reinforced plastic, and steel. In the past, unlined cast iron and asbestos cement pipes were frequently installed in distribution systems, and thus are important components of existing systems. Transmission mains are frequently 24inches (61cm) in diameter or greater, dual-purpose mains (which are used for both transmission and distribution) are normally 16–20 inches (40.6–50.8cm) in diameter, and distribution mains are usually 4–12inches (10.0–30.5cm) in diameter. Service lines and premise plumbing may be of virtually any material and are usually 1inch (2.54cm) in diameter or smaller. Premise plumbing and service lines have longer residence times, more stagnation, lower flow conditions, and elevated temperatures compared to the main distribution system. Inclusion of premise plumbing and service lines in the definition of a public water supply distribution system is not common because of their variable ownership, which ultimately affects who takes responsibility for their maintenance. Most drinking water utilities and regulatory bodies only take responsibility for the water delivered to the curb stop (Hudson 1991).
2.4.2 Pipe-Network Configurations:   
The two basic configurations for most water distribution systems are the branch and grid/loop .A branch system is similar to that of a tree branch, in which smaller pipes branch off larger pipes throughout the service area, such that the water can take only one pathway from the source to the consumer (Garg,  1994). This type of system is most frequently used in rural areas. A grid/looped system, which consist of connected pipe loops throughout the area to be served, are the most widely used configuration in large municipal areas. In this type of system there are several pathways that the water can follow from the source to the consumer. Looped systems provide a high degree of reliability should a line break occur because the break can be isolated with little impact on consumers outside the immediate area. Also, by keeping water moving looping reduces some of the problems associated with water stagnation, such as adverse reactions with the pipe walls, and it increases fire-fighting capability. However, loops can be dead-ends, and have associated water quality problems (Garg, 1994). Most systems are a combination of both looped and branched portions. Design of water networks is very much dependent on the specific topography and the street layout in a given community. Service mains should be located in every street.