**Forecast of Population for Water Supply**

In order to ensure proper planning for water supply systems, it is crucial to accurately forecast the future population growth. This allows water authorities and engineers to design and implement infrastructure projects that can meet the demands of the growing population. Several methods can be used to forecast population for water supply, including the arithmetic mean method, comparative method, and graphical method.

**Arithmetic Mean Method**

The arithmetic mean method is a simple and straightforward technique used for population forecasting. It involves calculating the average growth rate of the population over a certain period of time and then projecting this growth rate into the future. The steps involved in this method are as follows:

1. Determine the historical population data for a specific time period.
2. Calculate the average annual growth rate by dividing the change in population by the number of years.
3. Apply this average growth rate to the current population to estimate the future population.

The arithmetic mean method assumes a constant growth rate over time, which may not necessarily reflect the actual population growth pattern. However, it provides a quick estimate for water supply planning purposes.

**Comparative Method**

The comparative method involves comparing the population growth rates of different regions or areas with similar characteristics. This method relies on the assumption that areas with similar characteristics will experience similar population growth patterns. The steps involved in this method are as follows:

1. Identify regions or areas that have similar characteristics to the area of interest.
2. Determine the population growth rates of these similar regions over a specific time period.
3. Apply the average growth rate of the similar regions to the area of interest to forecast its future population.

The comparative method takes into account the unique characteristics of the area being studied and provides a more accurate estimate compared to the arithmetic mean method.

**Graphical Method**

The graphical method involves plotting the historical population data on a graph and analyzing the trend to forecast future population growth. This method allows for a visual representation of the population growth pattern and can help identify any irregularities or fluctuations. The steps involved in this method are as follows:

1. Plot the historical population data on a graph.
2. Analyze the trend of the population growth, considering factors such as growth rate, variability, and seasonality.
3. Extrapolate the trend into the future to estimate the future population.

The graphical method provides a more intuitive and visual approach to population forecasting, allowing for a better understanding of the population growth pattern.

**Conclusion**

In conclusion, the forecast of population for water supply can be done using the arithmetic mean method, comparative method, and graphical method. Each method has its own advantages and limitations, and the choice of method depends on the availability of data, time constraints, and the level of accuracy required. It is important to note that population forecasting is not an exact science, and the results should be regularly updated and revised based on actual population growth trends.