o_19f3m1n7k170b14e9u0oqipgu4a.pdf

industrial uses must also be added to the appropriate
node.
The 2 most common methods of maintaining system pressure
under widely varying flow rates are: (1) constantspeed
supply pumps and system elevated storage tanks,
which maintain essentially consistent system pressures,
or (2) constant-pressure, variable-speed, high-service
supply pumps, which maintain a constant system pressure
while meeting the varying demand for reclaimed water
by varying the pump speed. While each of these systems
has advantages and disadvantages, either system
will perform well and remains a matter of local choice.
The dual distribution system of the City of Altamonte
Springs, Florida operates with constant-speed supply
pumps and 2 elevated storage tanks, and pressures range
between 55 and 60 psi (380 kPa and 410 kPa). The urban
system of the Marin Municipal Water District, in
California, operates at a system pressure of 50 to 130
psi (350 kPa and 900 kPa), depending upon elevation
and distance from the point of supply, while Apopka,
Florida operates its reuse system at a pressure of 60 psi
(410 kPa).
The system should be designed with the flexibility to institute
some form of usage control when necessary and
provide for the potential resulting increase in the peak
hourly demand. One such form of usage control would be
to vary the days per week that schools, parks, golf
courses, and residential areas are irrigated. In addition,
large users, such as golf courses, will have a major impact
on the shape of the reclaimed water daily demand
curve, and hence on the peak hourly demand, depending
upon how the water is delivered to them. The reclaimed
water daily demand curve may be “flattened” and the peak
hourly demand reduced if the reclaimed water is discharged
to golf course ponds over a 24-hour period or
during the daytime hours when demand for residential
landscape irrigation is low. These methods of operation
can reduce peak demands, thereby reducing storage requirements,
pumping capacities, and pipe diameters. This
in turn, can reduce construction cost.
2.1.4 Using Reclaimed Water for Fire
Protection
Reclaimed water may be used for fire protection, but
this application requires additional design efforts (Snyder
et al., 2002). Urban potable water distribution systems
are typically sized based on fire flow requirements. In
residential areas, this can result in 6-inch diameter pipes
to support fire demands where 2-inch diameter pipes may
be sufficient to meet potable needs. Fire flow requirements
also increase the volume of water required to be
in storage at any given time. While this results in a very
robust distribution system, the increased pipe size and
storage required for fire flows results in increased residence
time within the distribution system, and a corresponding
potential reduction in reclaimed water quality.
In Rouse Hill, an independent community near Sydney,
Australia, reclaimed water lines are being sized to handle
fire flows, allowing potable line sizes to be reduced. Due
to a shortage of potable water supplies, the City of Cape
Coral, Florida, designed a dual distribution system supplied
by reclaimed water and surface water that provides
for fire protection and urban irrigation. This practice was
possible due to the fact that nonpotable service, including
the use of reclaimed water for fire protection, was part
of the planning of the development before construction.
However, these benefits come at the cost of elevating the
reclaimed water system to an essential service with reliability
equal to that of the potable water system. This in
turn, requires redundancy and emergency power with an
associated increase in cost. For these reasons, the City
has decided to not include fire protection in its future
reclaimed water distribution systems. This decision was
largely based on the fact that the inclusion of fire protection
limited operations of the reclaimed water distribution
system. Specifically, the limited operations included the
lack of ability to reduce the operating pressure and to
close valves in the distribution system.
In some cases, municipalities may be faced with replacing
existing potable water distribution systems, because
the pipe material is contributing to water quality problems.
In such instances, consideration could be given
to converting the existing network into a nonpotable distribution
system capable of providing fire protection and
installing a new, smaller network to handle potable demands.
Such an approach would require a comprehensive
cross connection control process to ensure all connections
between the potable and nonpotable system
were severed. Color-coding of below-ground piping also
poses a challenge. To date, no community has attempted
such a conversion. More often, the primary
means of fire protection is the potable water system,
with reclaimed water systems providing an additional
source of water for fire flows. In the City of St. Petersburg,
Florida, fire protection is shared between potable
and reclaimed water. In San Francisco, California, reclaimed
water is part of a dual system for fire protection
that includes high-rise buildings. Reclaimed water is also
available for fire protection in the Irvine Ranch Water
District, California. In some cases, site-specific investigations
may determine that reclaimed water is the most
cost-effective means of providing fire protection. The City
of Livermore, California, determined that using reclaimed
water for fire protection at airport hangers and a wholesale
warehouse store would be less expensive than up­
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