Water and Wastewater Engineering

Learning Objectives

A major issue in the design of water supply schemes is the collection, transport and distribution of water from the source. Collection of water from different sources, i.e., surface water versus groundwater, will differ for obvious reasons and was covered in Chapter 1.

The next major issue is the transport and distribution of water from the source or treatment plant to the community or service area. Different situations require different methods of transport and distribution. Distribution systems can be of three types: gravity, pumped or combined (Peavy, Rowe, and Tchobanoglous 1985).

Gravity distribution systems: If the source is elevated with respect to the community then water can be supplied directly by gravity. Examples are highland lakes or reservoirs that are used as water sources for many cities around the world such as New York and Mumbai.

Pumped distribution systems: If the source is at a lower elevation compared to the community or service area then it has to be pumped directly to the service area.

Combined distribution systems: If the source is at a lower elevation compared to the community or service area, then water can be pumped and stored in surface or elevated distribution reservoirs in the service area or adjacent to the service area resulting in a combined distribution system where gravity and pressure are used. Toronto pumps water out of Lake Ontario, treats the water and stores it in underground reservoirs and elevated reservoirs (called water towers) for further distribution to the service area.

Different types of distribution reservoirs can be built; they can be under-ground, over-ground or elevated. Water is then supplied from these distribution reservoirs to the community or to elevated storage reservoirs built within the community. Thus, combinations of direct gravity supply, pumped and/or elevated supplies are possible depending on the geography of the water source vis-à-vis the community. Definitional sketches of water supply conduits and service reservoirs are provided in Fair, Geyer, and Okun (1966).

The last issue in water supply systems is the analysis of pipe flows and head losses through the distribution system. Hardy–Cross method for analysis of pipe flow in distribution networks is covered in the last section.