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How to design a rectangular water tank?/ How to calculate the dimensions of water tank?

  Let us design a rectangular water tank for a family of  5 persons as shown below.



According to BIS standard IS 1172-1993,  the average water consumption per capita (LIG) in India is 135 liters/ day.



 The volume of water required ( in liters ) per day for 5 persons

   = [ per capita consumption /day × no. of persons.]

   = [ 135 liters × 5 nos.]

   = 675 liters.


Now, let us build a water tank having 3ft. depth as shown below.



A. Method - 1:

As you know, 

The volume of water tank

V1 = [ length (L) × breadth (B) × Depth ( D ) ]

   = [ L × B × 3 ft. ]

Here, the volume of the water tank is equal to the vol. of water consumed/day. Let us add 15% extra in the tank volume for the sump & emergency needs.

So, the required volume ( V ) 

 = [water consumption/day + 15% of daily consumption]

 = [ 675 liters + {( 15 ÷ 100) × 675 liters}]

= [ 675 liters. + 101.25 liters ]

= 776.25 liters.


As you know, 

  1 cu ft. = 28.3168 liters

  So, the vol. V of the water tank in cu ft.

   = [ 776. 25 ÷ 28.3168 ] cu ft.

   = 27.41 cu ft.


Now,    

   V =  [( L × B) × 3 ft. ]

 27.41cu ft. = [ (L × B )× 3 ft. ]

By cross multiplication,

(L × B ) = [27.41 cu ft. ÷ 3 ft.]

              = 9.14 sq ft.

You can choose any one of the lengths ( L ) or breadth ( B ), according to the available space for the tank construction.

Suppose if the ideal required length L= 4ft. then,

   (L × B ) = 9.14 sq. ft.

 ( 4ft.× B ) = 9.14 sq. ft.

 B = [9.14 sq. ft. ÷ 4 ft. ]

    = 2.285 ft.


The dimension of the water tank for holding water/ day

= L × B × H 




   = 4ft. × 2.285 ft. × 3ft.

   = 27.42 cu ft.

Note :

If you want to store the water for the 2days requirement, then you have to double any one dimension or recalculate for the 2 days water consumption.

For Eg., Let us take 2 times the breadth to double the vol. of the tank

 = [L × ( 2 × B) × D ]

 = [4ft. × (2 × 2.285 ft.) × 3 ft.]

= [ 4ft. × 4.57 ft. × 3 ft.]

= 54.84 cu ft. ( double the vol. of 27.42 cu ft.)


B. Method-2:

Let us assume the ideal required dimensions of the tank is as shown in the drawing.



Given data:

   Depth = D ft.

   Length L =  2 × depth = 2D

   Breadth B = 1.5 × depth = 1.5D


The required vol. of water tank 

    = 27.41 cu ft. (as calculated above. )

Now,

                 V =  [ L × B × D]

  27.41 cu ft. = [ ( 2D ) × ( 1.5D) × D ]

  27.41 cu ft. = [ 3 × D3  ]

    D3

        = [27.41 cu ft. ÷ 3]
        
        = 9.136 cu ft.

   D = [∛  9.136 cu ft.]

      = 2.09 ft.


Length = 2D = [2 × 2.09 ft.]

                     = 4.18 ft.


Breadth = 1.5D = [ 1.5 × 2.09 ft]

                         = 3.135 ft.


The dimension of the water tank for holding water/ day

  = L × B × H 





    = 4.18 ft. × 3.135 ft. × 2.09 ft.

To go through all types of structural design articles, click here.

Thank you for going through this article. Have a good day 😄.



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