Civil Engineering Reference
In-Depth Information
CHAPTER 22
Water Quality Control in
Distribution Systems
INTRODUCTION
If we look at the raw water supply (e.g., a river, reservoir, or aquifer) as the source
of raw material, and the treatment plant as the manufacturing facility, then the distri-
bution system is the product delivery system. In the same context, drinking water
would be considered a perishable product with a ''shelf life'' defined as the time
required to transport water from the end of treatment (manufacturing) to the customer's
tap.
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Consumers demand that the delivery system, particularly with products they con-
sume, be error-free. Microbial contamination can have enormous impacts on public
health and on the reputation of the company or organization whose product became
unsafe. A waterborne disease outbreak due to a failure in the distribution system will
have severe impacts on a water utility when the result includes ill customers, a boil-
water order, and a violation of federal law. Other consequences include damaged rep-
utation, lost public confidence, and, perhaps, fines or penalties imposed by a regulatory
authority.
The water quality aspects of distribution systems are increasingly important to reg-
ulators and utilities, as evidenced by several recent regulatory changes (see Chapter 1,
''Criteria and Standards for Potable Water Quality,'' for details). The Total Coliform
Rule established, for the first time, a nationwide regulation requiring every community
to have an approved plan for analyzing bacteriological quality at various points in the
distribution system and requires public notification whenever these bacteriological
standards for are not met. The Lead and Copper Rule requires that samples be collected
in the distribution system to monitor concentrations of lead and copper. The
Disinfectant / Disinfection By-Product Rule requires measurements of disinfectant re-
siduals and DBPs in the distribution system. No longer is it considered adequate to
simply monitor the quality of the treated water as it leaves the water treatment plant.
As research has expanded our knowledge of distribution system water quality and
consumers have demanded higher-quality drinking water, the number of issues involv-
ing water quality has increased. Traditional distribution-related water quality concerns
such as hardness, corrosion, cross-connection control, prevention of waterborne dis-
ease, and maintenance of disinfectant residual have been supplemented with emerging
concerns such as biofilms, bacterial regrowth, maximum disinfectant residual levels
(MRDLs), the dynamics of DBPs in the distribution system, and distribution of ground-
water supplies being disinfected for the first time. While in the past it may have been
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