Durable GRP water storage tanks manufactured as a single-piece unit, ideal where access allows for straightforward installation and a robust, low-maintenance storage solution.
GRP water storage tanks supplied in two sections for easier access and installation in restricted spaces, while still providing a strong, reliable and long-lasting water storage solution.
High-quality sectional GRP water storage tanks, manufactured in the UK by Decca Tanks. Designed for durability, flexibility and reliable water storage across commercial, industrial and residential applications.
GRP cold water storage tanks and a separate dry equipment compartment moulded into a single enclosure, for sites with no plant room to spare and where the tank, its controls and its pipework need to arrive protected.
GRP housings and walk-in enclosures for housing equipment, controls and metering outdoors, rated IP55 with stainless steel hinges and available in single skin or ply-cored construction.
Float valves, overflows, tank connectors, drain valves and level switches for Decca tanks, supplied individually so a single fitting can be replaced without changing the tank.
Your tank details are included with this enquiry. Add your contact details below. Fields marked * are required.
Share your figures, drawing or known requirements. Decca helps select the tank, reviews the proposed dimensions and connections, and confirms the manufacturing and supply scope. Where installation is included, the quotation will set out the agreed testing, cleaning, disinfection and handover requirements. The responsible designer retains the system-demand and structural design checks.
02 / Your live capacity breakdown
Your inputs. Your capacity breakdown.
See the dimensions, water levels and working behind your litres. These figures update when you change the calculator above.
Choose your tank construction and enter valid dimensions and connections in the calculator to see your breakdown.
Inputs from your calculator
Tank selection
Starting point
Entered requirement
Room allowances
Capacity basis
Water duty
Inlet arrangement
Overflow
Outlet
Dimensions & water levels used
Internal L × W × H
External tank body
Freeboard / top deduction
Top water depth
Below the usable level
Usable water depth
01 / Nominal
Full tank capacity
02 / Actual
Water at operating level
Includes the water below the lower usable level.
03 / Actual usable
Water available to use
Excludes the water below the lower usable level.
04 / Effective
For the agreed usable limits
Effective capacity uses the same usable limits only where they suit the specified sprinkler or wet-riser system. The system designer confirms those limits.
Dimensions in the working are millimetres; dividing cubic millimetres by 1,000,000 gives litres. The calculator uses full precision; displayed litres are rounded to whole numbers. Use Calculate capacity above to confirm the current figures for your enquiry or technical sheet.
03 / The details that change the litres
Connections change usable storage.
Outlet elevation, required submergence and pump-protection settings determine the lower usable level. A different fitting arrangement may change the result within the same tank.
Straight outlet
The outlet and required water cover above it set the usable limit.
Downturn elbow
A downward-facing intake can change the intake position and required submergence.
Vortex inhibitor
An engineered anti-vortex arrangement can change the required water cover.
These drawings explain arrangements only. They do not prescribe fitting dimensions or guarantee a particular bottom allowance.
Top water level & freeboard
Freeboard is the airspace above the water line to the underside of the cover. It is different from the air gap at a mains-water inlet.
Raised inlet chambers
A chamber houses the inlet valve above the main cover and can allow a higher top water level. Check total height and valve access; it does not give every tank a fixed extra capacity.
Your early-warning selection
For one-piece and two-piece tanks, the early-warning connection starts at 20 mm. You can select None in Connections; the calculation, enquiry and technical sheet follow your selection.
Decca must confirm the final warning and overflow arrangement for your tank and application.
Check installation and maintenance access, external flanges, insulation, supports, headroom and the route into the building. Required clearances depend on the construction.
TIF: access size is not water volume
Water can occupy the panel faces beyond internal flanges. Do not use the clear-access dimensions alone to calculate capacity. Decca checks the selected construction and internal geometry.
Divided tanks: specify each side
Give the total capacity and required capacity in each compartment. The system designer must confirm the storage needed during cleaning or maintenance.
Choose the construction with Decca
Delivery route and installation access can be as important as litres.
One-pieceTwo-pieceSectional IFB / EFB / IF / TIF
Use the construction selector in your enquiry to tell us what you have in mind. We will review the requirement against suitable tank options, access and available dimensions.
Use the basis stated by the system designer or specification: nominal, actual, actual usable or effective. If you are unsure, select “Not sure” in the calculator and include the specification in your enquiry.
Are the calculator dimensions internal or external?
Enter sectional planning dimensions in metres. The calculator adjusts them for the selected construction and shows the internal water-retaining and external tank sizes. DP internal sizes are approximate. Space mode deducts your entered installation allowances before checking the available tank size.
Does a 12,000 litre tank give me 12,000 litres to use?
Not necessarily. The worked example holds 12,000 litres brim-full, 10,800 litres to its assumed top water level and 9,000 litres between its assumed usable limits. Your levels may be different.
Can I use this to size my building’s water demand?
This tool converts dimensions and specified water levels into geometric volumes. The system designer establishes demand, reserve and the required storage for the application.
Can an inlet chamber increase the capacity?
It can allow a higher top water level by housing the inlet valve above the main cover. The achievable level depends on the inlet, overflow and warning arrangements. Allow for chamber height and service access.
What should I send for a quotation?
Send required litres and capacity basis, water duty, available footprint and headroom, access restrictions, preferred construction, compartments and known connection or operating-level requirements. The button below carries your calculator inputs into the enquiry.
