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288 Chapter 8 Pumping, Storage, and Dual Water Systems
8.7.1 Background

In the 18th and early 19th centuries, the demand for protection against fire and the great
conflagrations and loss of life that they brought predicated the provision of water distribu-
tion systems designed for fire protection. Only later were these distribution systems put
into service for commercial and then residential use, which led to the subsequent develop-
ment of the water closet and sewerage systems.
That our present distribution systems are delivering water of exceedingly poor qual-
ity today, almost without regard to the water’s source, treatment, or distribution, has
been made manifest by the vast literature emerging from every corner of the water sup-
ply scene. The American Water Works Association (AWWA) has shown considerable
awareness of the problems. Its annual water quality technology conferences have each
had more than 100 papers identifying the problems. Some 40 classes of problems are set
out by AWWA, with recommendations for individual utilities to assess their own partic-
ular problems and find their own answers. But relatively few utilities have the appropri-
ate staff or financial resources to undertake the required studies and address each of the
many problems.
The recommended practice of frequent flushing of the distribution systems has been
widely adopted, but it hardly addresses the problems. Flushing is costly in personnel and
extremely wasteful of treated drinking water, which is discharged to stormwater sewerage
systems. In addition, frequent flushing is not very effective in keeping the pipes free from
biofilm growths on pipe walls and maintaining hydraulic capacity

8.7.2 The Nature of the Problems with Drinking Water Quality
The critical problem is that fire protection requires there to be many hydrants throughout a
city, which have to have the capacity to deliver relatively high flow rates at all times and at
all locations throughout the area. Pipe sizes were initially a minimum of 6 in. (150 mm),
but today this has increased in many communities to a minimum of 8 in. (200 mm).
Because fires are infrequent, the velocity of the water in the network is almost always
slow, resulting in residence times of months between when the water is treated and when it
arrives at the taps of consumers in the outer regions of the service area. Recent tracer studies
by the University of North Carolina in two of the larger cities in the state revealed residence
times of more than 10 days. Such times make adequate chlorine residuals at the tap unlikely.
The inadequacy of disinfection, with the resulting risk of microbial exposure at the
tap, is not the most troublesome problem arising from ineffective disinfection. In attempt-
ing to provide adequate disinfection despite the poor conditions in the pipelines,
providers considerably increase the chlorine dose, resulting in increased levels of disin-
fection by-products (DBPs) through reactions with both chemical and microbial contami-
nants in the water.
Trihalomethanes (THMs) and haloacetic acids (HAAs) are the only two DBPs that
are being regulated by the U.S. Environmental Protection Agency (EPA), but then with
great difficulty. Their maximum contaminant levels (MCLs) were epidemiologically un-
certain, as indicated by the arbitrary adoption of a THM level of a “round” 0.10 mg/L in
1979. This figure was reduced recently, based in large part on the ability of utilities to
reach a lower level.
The DBP problem is much more difficult to manage than is evident from recent re-
search. As shown later, many more contaminants are present in drinking water networks
than are recognized today as potential reactants with the chlorine present in the water and
therefore there are many more other DBPs that need to be regulated.