1 March 1997
a. Reservoirs and standpipes. In public and private communities, significant emphasis has been placed
on making water storage facilities attractive so as not to distract from the appearance of the community.
This has lead to the development of a variety of roof designs. On military sites, the most economical
functional roof will be used except where the setting requires a more aesthetically pleasing design. A
column-and-rafter supported steel roof, with columns supported by footings rather than the tank walls, is
generally the most economical type for a reservoir and can be used on a standpipe less than 50 feet in
height. Self-supporting (supported by the tank) cone roofs have proven to be inexpensive and quite
functional for small diameter reservoirs and standpipes. Roofs supported by the tank are generally dome
or umbrella shaped steel roofs and provide a smooth appearance. Roof styles for welded steel tanks
include conical, umbrella, dome, and ellipsoidal designs. Bolted steel tanks commonly have conical steel
roofs or aluminum domes. Aluminum domes have also been used for welded steel and concrete tanks
and reservoirs. Advantages that aluminum may have over other roof materials (depending on the individual
situation) are improved corrosion resistance, light weight, lower costs, easier erection, enhanced aesthetics,
and less maintenance. Dead weights of metal roofs average 140 N/m 2 (3 lbs/ft 2) or less for aluminum, 180
N/m2 (3.8 lbs/ft 2) for bolted steel, and 360 N/m 2 (7.6 lbs/ft 2) for welded steel. Cast-in-place and precast
concrete (dome and flat) roofs have also been provided for concrete tanks - flat concrete roofs are used for
buried tanks when the ground above it is needed for other uses.
b. Elevated tanks. Roofs for elevated tanks are generally a self-supporting integral part of the tank.
Self-supporting dome and umbrella designs have been used for smaller tanks.
3. ALTITUDE VALVES. All storage tanks will be provided with altitude valves to prevent overflows. These
altitude valves will be installed in concrete pits having provision for draining either by gravity or pumping.
Drains will not be connected to sanitary sewers. Every precaution will be taken to prevent the collection of
any source in valve pits.
4. INSTRUMENTATION AND CONTROL. Storage measurements are used for monitoring, inventory, and
system controls. Elevated and ground storage measurements will be made by pressure sensitive
instruments directly connected by static pressure lines at points of no flow. Underground storage
measurements will be made by air bubbler back pressure sensitive instruments or by float actuated
instruments. The direct pressure measurements of elevated tanks will be suppressed to readout only the
water depth in the elevated bowl. High and low level pressure sensitive switches will be used for alarm
status monitoring and for pump cut-off controls. Intermediate level switches, pressure or float actuated, will
be used for normal pump controls. Metering, monitoring, and pump control requirements at some point
remote from storage must use level telemetry instruments. Telemetering over local direct wire
communications facilities will use 15 second time duration or impulse duration telemetering equipment.
Telemetering over leased telephone lines often requires the introduction of a tone transmitter and receiver
keyed by the time-impulse telemetering equipment. High storage level will initiate the shutdown of supply
pumping units and actuation of an overflow alarm in that order. Low storage level will initiate startup of
supply pumping or well pumping units or distribution pumping unit shutdown.
5. DISINFECTION. Potable water storage facilities, associated piping, and ancillary equipment must be
disinfected before use. Disinfection will be accomplished following procedures and requirements of AWWA
C652. In no event will any of the above equipment or facilities be placed in service prior to verification by the
supporting medical authority, by bacteriological tests, that disinfection has been accomplished.
6. DESIGN ANALYSES. The design analyses will set forth the basis by which storage capacities and
locations have been determined. Except where standard specifications for tanks or towers are used, the
analyses will show the method by which the structural adequacy of the unit has been determined.