Population forecasting methods are needed to design water supply systems for the expected future population in the design period, rather than just the current population. Short term forecasting methods include arithmetic progression, geometric progression, and decreasing rate of increase models, while long term methods include comparative, ratio & correlation, component, and logistic curve fitting techniques. Arithmetic progression assumes a constant rate of population increase over time.

1. POPULATION FORECASTING
Since the water
supply systems are designed for a certain design period, instead of
present
population, population expected in the design period must be considered
in the design of
water supply systems
(A)Short term methods;
Arithmetic progression

Geometric progression
.ller Bankası method

Decreasing rate of increase

.Graphical extension
(B)Long term methods;
(1)Comparative method
(2)Ratio & correlation method
(3)Component method
(4)Logistic method (mathematical curve fitting
(1)ARITHMETIC PROGRESSION; Rate of population increase is
constant and expression is dp/dt=Ka
Where K is an arithmetic constant

2. The formula is;P_future=P_last+(Ka) (t_future-t_last)
and Ka