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Overhead Tank Capacity: Calculation:Ranchi

I am staying at Ranchi, the capital of Jharkhand, in a building comprising of 34 flats. I would like to know the minimum storage capacity of overhead water tanks. Please give the details of calculation.

Note: - There is no underground water tank. The overhead tanks are to be fed through deep well boring and used to service all the needs of the residents.

Sanjay Verma, Ranchi.




Dear Sanjay Verma,

To assess the capacity of water tank, certain assumptions are to be made.
1. Assuming 4 dwellers residing in 1 flat.

2. Assuming each will consume about 200 litres of water per day in peak season i.e. in summer.

Quantity of storage per day = 34 flats X 4 X 200= 27200 i.e. approx. 28000 lit per day.

At least 4 tanks will be required to cater the demand then.

Capacity required for each tank= 28000/4 = 7000 litres.
Concrete tank will be more useful to decide the sizes= 7 cum capacity.
Sizes approx. for each tank = 2.5 X2.2X.1.3 (depth).


Lalit Bokolia
Joint Director
National River Conservation Directorate
Ministry of Environment and Forests
Government of India


Dear Sanjay Verma,

The overhead tank should supply about 34 X 1500 litres (assuming 5 persons in a house) i.e, 51,000 litres of water per day for comfortable use of water for all purposes for the whole complex. If it is filled twice a day, the tank capacity can be 26,000 litres or 26 cubic meters.

S.V.Vijaya Kumar


Dear Sanjay Verma,

Calculations for designed capacity of Tank & Pump

Total no. of flats = 34
Av.population = 5 persons/flat (taken)
Total population = 34X5 =170

For Ranchi

Av. Domestic water consumption for Indian town with full flushing system = 200 lt/head/day
(As per IS: 1172-1993)
Av. Daily Demand (ADD) of Water = Av. water consumption X population = 200 X 170 = 34000 lt/day
Max. Daily Demand (MDD) of Water @180% of ADD = 180/100 X 34000 = 61200 lt/day

Designed capacity of Tank (minimum) = MDD of Water = 61200 lt.
Designed capacity of Pump = 2 times of ADD = 34000 X 2 = 68000 lt/day
Designed capacity of Pump = 24/8 X 68000 = 204000 lt/day (say, operated for 8 hrs/day)

Thank you

S. Halder
Assistant Engineer (Agri- Irri)
Water Investigation & Development Department
Government of West Bengal

4. Design capacity?

Are you sure of what you're saying, always saying design capacity? Where's the design now? Dimensions? Thickness? Height of the tank from the slab? The plan view? Where?


Dear Sanjay Verma,

As per the Urban Ministry's calculation 135 litres is the requirement /person/day. Please calculate for the no. of persons staying in the Apt. bldg. in 34 flats. For an approximation 4 persons are estimated to live in a flat. So 34x4x134 litres is to be kept in the overhead tank. Since the Apt bldg has a pumping system you do not need a Reserve except when your pumps



6. Find your input very useful


I find your input very useful. The approach is very logical and I think 140 liters per head per day is a more reasonable estimate, even considering some amount of losses.


Dear Sanjay Verma,

For designing a storage tank one of the important factor is the average daily usage of water per capita, which is different for different areas depending upon the

1. Availability of water
2. Climatic parameters like temperature, rainfall etc.
3. Life style of the population etc. For example deserts people water need is less as compared to the barrage area people because desert people have less accessibility to water.

First you should know the per day per capita demand for water, then estimate the population for whole building, then decide for how much time/years you are going to design the storage tank, then decide for how many days you want to store the water, consider the population growth rate and find the future population need/demand by the formula:

Pp (1 + n/100) ^N (This formula will give you the future population) in which Pp = Current Population
n = Population growth rate
N= Numbers of years for which you want to design

I hope above hints will help you. If you need further help, then do not hesitate to contact me.

Kind regards,

Engr. Habib ur Rehman
Irrigation and Water Management Advisor
Catholic Relief Services
Islamabad, Pakistan


Dear Sanjay Verma,

The capacity of overhead tank shall be calculated on the basis of residents. 34 flats x 5 residents per flat x 200 liters/capita water = 34000 liters. You may consider a tank of size 4m x 4m x 2m + 0.3m free board. This way, the roof slab shall be designed for a load of 2.5 tons/sqm.

With best regards,

Taral Kumar
Executive Director
Akar Impex Pvt. Ltd.
E-9, Sector 6, Noida
Uttar Pradesh

9. Need clarifications about over head tanks in urban context

Dear Sir,

This is with respect to your comment in July 2008 to Sanjay. I want to know some of the following aspects of size of overhead tanks.

In an urban location, if we want to go for more storage of water or use a bigger O.H. tank: How we should calculate the load on the roof due to O.H. tank? What is the limit on the load bearing capacity of the roof? How to arrive at the limiting value of the tank size to be placed on building roof?

Kindly reply
Thanks and regards,

10. Request for your contact details


I am a diploma holder in civil, but  do not have a job. I request you to provide your mobile or email id for contacting you. Looking forward



Dear Sanjay Verma,

It is rather difficult to give advice on the size of the overhead tank, unless there is some built in control on the rational distribution of the water collected in it. I suggest the following.

1. The actual size will depend on the daily yield of the bore well. Consult a local hydrogeologist to determine the specific capacity of the well and the daily sustainable yield of the well.

2. We all have tendency to be profligate and wasteful, when it comes to use of a common source. This can be taken care of by:

a) Metering the water entering each flat and charging for it from the flat owner or

b) Designing the tank with separate compartments and separate pipelines (in this case 34) for supplying each flat.

The latter solution is better as some of the flat owners might be in a position to pay more and this will empty the tank. This solution has higher capital costs but no recurring headaches for the Secretary of the housing society.


Formerly Director Grade Scientist
National Geophysical Research Institute, Hyderabad & Emeritus Scientist
Council of Scientific and Industrial Research


Dear Mr. Varma

Calculation as per National Building Code.
Total water supply - 135 liter per person per day
Persons per flat 5. You may actually count the total number. Consider which ever is higher.
Total capacity of tank = One day storage for Total water demand
Capacity = Total population X 135 liter
Please contact us if you need more information

Viraj Envirozing India Pvt. Ltd.
21 Radhakrishna, Near SBI, Paud Road, Pune 411038


You want to use the overhead tank as a balancing reservoir. Design of balancing reservoir is simple, calculate the cumulative hourly inflow (pumped flow) and cumulative hourly outflow (based on demand pattern) to the OHT. The summation of maximum shortfall and maximum storage gives the required storage capacity.

You can get it from any standard book on water supply by Birdie/Garg/Hammer.

You have to correctly estimate the demand pattern which governs the outflow from the tank. You have a very small population, so peaks have to be chosen carefully. As a back-up you can provide level controllers between pumps start-stop and OHT levels. That will always ensure proper storage.

14. level controllers

Dear Sandeepan Chowdhuri

Would you please elaborate on "level controllers between pumps start-stop and OHT levels"

Thanks ,


15. How to decide dimensions of an underground tank

For my project purpose I'm designing an underground tank. I want to know the details about how to decide on the tank dimensions. Is there any code book preferred for that?

Volume of the water = 3105 m3.

Can you suggest ways to decide the dimensions of the underground tank for the said volume?


16. Want requirements for designing an 200,000 litres over head tank

I am Saleem Basha from K.S.RM. College of Engg, Kadapa, Andhra Pradesh.

Sir I want to know the requirements for designing an over head tank with the capacity of 200,000 litres. Please explain everything to me clearly with calculations.

17. Need calculations for overhead water tanks for a township

For a township project whose water consumption demand is 5 MLD, how many overhead tanks and of what dimensions are required?

Please elaborate with calculations involved.

18. Calculating tank capaciy for a population of about 10524774

I want to know the amount of water a tank can store for a population of 10524774 and the advantages of different types of tanks.

19. How to ensure equal supply to all?

How to ensure equal supply to all when it comes to overhead tanks?

20. I know how to design a water tank

I know how to design a water tank. I am a architect.

21. Need suggestions for designing an overhead tank for a project

Sir/ Madam,

For my project purpose I'm designing an overhead tank for rural as well as urban areas. Would like to know the points to be included. Is there any code book / reference books/ guide books available? I believe that the maximum permission of one overhead tank is max 200,000 liters.

Please guide.

22. Want the calculation to build underground water tank

Dear sir,

Please tell me the calculation to build underground water tank 

23. Need help with design for OHT of 50,000 ltrs capacity


I am planning to have a water storage over head tank for my farm with the capacity of 50,000 ltrs.I have a provision of a borewell in my farm. The main purpose to build this OHT is to manage water scarcity problems during summer. Need help with the OHT design details & approximate cost to get it built.


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