Water Demand

By Shreya Laddha|Updated : December 2nd, 2021

Through Champion Study Plan for GATE Civil Engineering (CE) 2022, we are providing Water Demand study notes and other important materials on every topic of each subject.

These topic-wise study notes are useful for the preparation of various upcoming exams like GATE CivilIESBARCISROSSC-JEState Engineering Services examinations and other important upcoming competitive exams.

This article contains fundamental notes on the "Water Demand" topic of the "Environmental Engineering" subject.

Water Demand

 Fire Demand

 Rate of fire demand is sometimes treated as a function of population and is worked out on the basis of empirical formulas:

(i) As per GO Fire Demand

 Q = 100(P)1/2 

(ii) Kuichling’s Formula


 Where Q = Amount of water required in liters/minute.

 P = Population in thousand.

(iii) Freeman Formula


(iv) National Board of Fire Under Writers Formula

 (a) For a central congested high valued city

 (i) Where population < 200000


 (ii) where population > 200000

 Q = 54600 lit/minute for first fire

 and Q=9100 to 36,400 lit/minute for a second fire.

 (b) For a residential city.

 (i) Small or low building,

 Q=2,200 lit/minutes.

 (ii) Larger or higher buildings,

 Q=4500 lit/minute.

 (iii) High value residences, apartments, tenements

 Q=7650 to 13,500 lit/minute.

 (iv) Three storeyed buildings in density built-up sections,

 Q=27000 lit/minute.

(iv) Buston’s Formula


The probability of occurrence of a fire, which, in turn, depends upon the type of the city served, has been taken into consideration in developing a above formula on the basis of actual water consumption in fire fighting for Jabalpur city of India. The formula is given as



 R = Recurrence interval of fire i.e., period of occurrence of fire in years, which will be different for residential, commercial and industrial cities.


Per Capita Demand (q)



Assessment of Normal Variation

(i) byjusexamprep 

(ii) byjusexamprep 

(iii) byjusexamprep 

(iv) byjusexamprep 

(v) byjusexamprep

(vi) byjusexamprep


Population forecasting Methods

(i) Arithmetic increase method



 byjusexamprep Prospective or forecasted population after n decades from the present (i.e., last known census)

 byjusexamprep Population at present (i.e., last known census)

 byjusexamprep Number of decades between now & future.

 byjusexamprep Average (arithmetic mean) of population increases in the known decades.


(ii) Geometric Increase Method



 byjusexamprep Initial population.

 byjusexamprep Future population after ‘n’ decades.

 byjusexamprep Assumed growth rate (%).



 byjusexamprep Final known population

 byjusexamprep Initial known population

 byjusexamprep Number of decades (period) between byjusexamprep and byjusexamprep 



(iii) Incremental Increases Method



 byjusexamprep Average increase of population of known decades

 byjusexamprep Average of incremental increases of the known decades.


(iv) Decreasing rate of growth method

 Since the rate of increase in the population goes on reducing, as the cities reach towards saturation, a method which makes use of the decrease in the percentage increase, in many times used, and gives quite rational results. In this method, the average decrease in the percentage increase is worked out, and is then subtracted from the latest percentage increase for each successive decade. This method is, however, applicable only in cases, where the rate of growth shows a downward trend.


(v) Logistic Curve Method

 (a) byjusexamprep 


 byjusexamprep Population of the start point.

 byjusexamprep Saturation population

 byjusexamprep Population at any time t from the origin.

 byjusexamprep Constant.

 (b) byjusexamprep 

 (c) byjusexamprep 

 (d) byjusexamprep 

 (e) byjusexamprep 



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