1 March 1997
DESIGN AND CONSTRUCTION OF WATER STORAGE FACILITIES
1. CONSTRUCTION MATERIALS.
(1) General. Reinforced concrete is popular for construction of reservoirs and standpipes because it
produces structures with long service lives and which require little maintenance. Such reservoirs and tanks
can be below or partially below ground with the above ground portion architecturally enhanced if needed by
(2) Prestressed concrete tanks. Standards for the design and construction of wire-wound circular
prestressed-concrete water tanks are provided by AWWA D110. Such tanks can be constructed of cast-in-
place concrete, shotcrete, or precast concrete. An interior, vertically reinforced concrete wall encases a
mechanically lock seamed steel diaphragm, which provides water-tight containment. The wall and
diaphragm is covered with shotcrete and continuously stressed wire is wrapped in layers around the
structure as the shotcrete is applied. A painted or decorative coating can be applied to the exterior.
(1) General. Steel reservoirs and standpipes weigh about one-eighth as much as concrete tanks
and are generally more economical for remote sites where it is difficult to transport materials. The lower
weight will also reduce the foundation requirements.
(2) Welded tanks. All elevated steel tanks and many standpipes and reservoirs are of welded steel
construction, allowing them to be dismantled, moved, and reconstructed. Welded tanks have been used
since the 1930's for water storage and have completely replaced riveted construction. Standards for design
and construction of welded water tanks, with capacities of 19,000 L to 11 ML (5,000 gal to 3 Mgal), are
provided in AWWA D100.
(3) Bolted tanks. Factory-coated bolted steel water tanks became popular in the 1970's for
standpipes and reservoirs. They utilize steel panels, of lighter gauge than welded tanks, that are bolted
together onsite using gaskets or sealants for sealing the joints. Compared to welded tanks, they are easy
to dismantle and relocate. Standard capacities range from 15,000 L to 6.8 ML (4,000 gal to 2.5 Mgal).
Standards for design and construction of bolted steel tanks are provided in AWWA D103.
c. Composite. Another type of elevated tank is the composite tank which consists of a welded steel tank
supported by a reinforced concrete pedestal of tower. Design and construction guidance are provided in
Steel Plate Fabricators Guideline Specification for Composite Elevated Water Tanks.
2. ROOFS AND COVERS. All treated water tanks and reservoirs must be covered to prevent
contamination by dust, birds, leaves, and insects. These covers will be, insofar as possible, watertight at all
locations except vent openings. Special attention should be directed toward making all doors and
manholes watertight. Vent openings must be protected to prevent the entry of birds and insects; and vent
screens should be kept free of ice or debris so that air can enter or leave the storage area as temperature
and water levels vary. All overflows or other drain lines must be designed so as to eliminate the possibility
of flood waters or other contamination coming in contact with the treated water. Covers also protect the
stored water from sunlight, thus inhibiting the growth of algae. Further prevention of algae growth or
bacterial contamination, due to the depletion of the chlorine residual, can be obtained by maintaining
sufficient flow through the tank or reservoir so that stored water does not become stagnant. Minimal flows
through the system also help to prevent ice buildup during cold periods.