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Chapter 6

Water Distribution Systems:

Components, Design, and

Operation

6.1 DISTRIBUTION SYSTEMS
Apart from a few scattered taps and takeoffs along their feeder conduits, distribution sys-
tems for public water supplies are networks of pipes within networks of streets. Street plan,
topography, and location of supply works, together with service storage, determine the
type of distribution system and the type of flow through it. Although service reservoirs are
often placed along lines of supply, where they may usefully reduce conduit pressures, their
principal purpose is to satisfy network requirements. Accordingly they are, in fact, compo-
nents of the distribution system, not of the transmission system.

6.1.1 One- and Two-Directional Flow
The type of flow creates four systems, as sketched in Fig. 6.1. Hydraulic grade lines and
residual pressures within the areas served, together with the volume of distribution storage,
govern the pipe sizes within the network. It is plain that flows from opposite directions in-
crease system capacity. With two-directional flow in the main arteries, a pumped or gravity
supply, or a service reservoir, feeds into opposite ends of the distribution system or through
the system to elevated storage in a reservoir, tank, or standpipe situated at the far end of the
area of greatest water demand. Volume and location of service storage depend on topogra-
phy and water needs.

6.1.2 Distribution Patterns
Two distribution patterns emerge from the street plan: (a) a branching pattern on the
outskirts of the community, in which ribbon development follows the primary arteries
of roads (Fig. 6.2a), and (b) a gridiron pattern within the built-up portions of the com-
munity where streets crisscross and water mains are interconnected (Figs. 6.2b and
6.2c). Hydraulically, the gridiron system has the advantage of delivering water to any
spot from more than one direction and of avoiding dead-ends. The system is strength-
ened by substituting for a central feeder a loop or belt of feeders that supply water to
the congested, or high-value, district from at least two directions. This more or less

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