Composite Elevated Storage Tank (CET)

DEFINITION: An elevated welded carbon-steel water storage tank supported by a large diameter steel-reinforced concrete support tower that extends vertically from the steel-reinforced concrete foundation as a circular concrete support structure/wall and has special horizontal and vertical rustication patterns formed into the exterior of the tower.

Positive Uses (when it's best)

  • Most modern style, some believe the most aesthetically pleasing, and others feel the securest with least liability
  • Areas where future repainting is either limited or more frequent (tight sights or salty environment)
  • Most common & typically most economical style in capacities greater that 1,000,000 gallons

Highlights & Advantages (over other styles)

  • The Composite Elevated Tank is an attractive, low maintenance and durable structure combining an efficient use of reinforced concrete for the support pedestal and welded steel for a watertight storage tank
  • Cost efficiency is gained by utilizing the valuable strength characteristics of each material; the tensile strength of steel for the water containment vessel and the compressive strength of concrete as the support column for the tank
  • No coating system required for concrete shaft and thus less long-term maintenance (reduced surface area for painting)
  • Interior ladders and piping protects against weather and vandalism and easily allows for pipe insulation
  • Two styles of typical roofs: Conical or Dome
  • Architectural Rustications highlight the concrete column.  These rustications are placed vertically and horizontally at the edge of concrete forms to blend concrete appearance and hide construction joints

Special Features (bonus part of asset)

  • Unauthorized access to the tank contents and vandal's graffiti are eliminated by pad-locked doors plus anti-graffiti coatings available; generally used for the first 20 feet of concrete shaft.
  • The shaft can be furnished with a 10' or 12' wide (depending on column diameter and the owner's needs) overhead door for easy access making it possible for the base area of the shaft to have ample storage for valve assemblies, pumps, and equipment or multi-purpose uses such as office space, file storage, and possibly multiple floors with windows.
  • Reinforced concrete pedestal support shaft offers ‘Severe Weather' protection for nearby employees, personnel, or neighbors as well as an uninterrupted ground silhouette (shadow on the ground).

Standard Sizes (others available but may be at a premium)

  • Reference the table 500,000 to 3,000,000

Standard Accessories
American Water Works Association (AWWA D107 & D102)

  • Steel frost-proof pressure/vacuum relief vent designed for maximum protection
  • (1) 24" diameter roof hatch with hinged cover and hasp
  • (1) 24" diameter roof hatch bolted for attachment of exhaust fan
  • (1) 24" diameter access tube roof hatch
  • (1) 24" diameter tank floor manhole
  • (1) 24" x 36" removable access hatch at top of supporting shaft
  • (1) 18" x 24" diameter manhole in base of access tube
  • (1) 24" diameter painter hatch at top of composite shaft
  • Purchaser specified inlet/outlet piping with expansion joint
  • Shaft-supported stainless steel overflow pipe to grade level with concrete splash pad
  • All ladders, walkways, handrails and attachments inside the shaft are galvanized
  • Rest seats at desired intervals
  • Supporting shaft and access tube ladders with OSHA compliant safety climb devices
  • Upper shaft walkway with OSHA compliant handrail
  • Grounding for minimizing lightning damage
  • Personnel door in base of supporting shaft
  • Metal drip pan drain under access tube
  • Gravel floor inside shaft

Elective Accessories
Collective in the Water Tank Industry

  • Tank drain for washouts
  • Larger diameter manholes, hatches, and access tube
  • Complete internal seal welding
  • Overhead rolling door with automatic closer
  • Intermediate rest platforms with OSHA compliant handrails
  • Roof handrail
  • Aluminum or custom roof vent
  • Cellular antenna supports and provisions
  • Painted logo, lettering, and custom graphics
  • FAA lighting
  • Insulated tank piping
  • Piping in base of shaft - bypass lines, altitude valve, service pumps, etc.
  • Additional free-span floors
  • Masonry block building in base of shaft
  • Overflow flap valve
  • High water elevation/pressure gauge
  • Concrete floor inside shaft
  • Instrumentation, control room, & cathodic protection
  • Solar powered or other type of mixing system
  • Additional security or ornamental lighting
  • Specialty trim or customized design

Specifications & Standard Tank Drawing

Caldwell Drawings & Specs

Standard Sizes : CET

(US Gallons)
Head Range
Tank Diameter
Pedestal Diameter
500,000 35' 50' 30'
500,000 30' 58' 30'
750,000 30' 74' 40'
750,000 35' 64' 36'
1,000,00035' 74' 40'
1,000,000 40' 68' 36'
1,250,000 34' 86' 48'
1,500,000 39.5' 86' 48'
2,000,000 42' 98' 48'
2,500,000 45' 104' 56'
3,000,000 45' 116' 64'

Surveys from Actual Caldwell Tank projects

Case Studies for Actual Caldwell Tank projects

Caldwell Connect