Environmental Engineering - Water Demand & Sources of Water Complete Study Notes

By Sidharth Jain|Updated : March 1st, 2022

Complete coverage of the APPSC AE Exam syllabus is a very important aspect for any competitive examination but before that important subjects and their concept must be covered thoroughly. In this article, we are going to discuss the Water Demand & Sources of Water topic which is very useful for APPSC AE Exams.

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


(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 the 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)

 byjusexamprepNumber 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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