WATER SUPPLY AND SANITARY OBJECTIVE GUIDE

• The vertical wells provided along the banks of a river to draw ground water in dry season are called infiltration wells.
• When in the pervious strata, the surface of the water surrounding the well is at atmospheric pressure the well is known as gravity well.
• An artesian spring is formed when a porous strata gets enclosed between two impervius strata.
• The quantity of water avialable from infiltration gallery depends upon the size of gallery, nature of soil and yield of source.
• The portio of soil through which lateral movement of water takes place is called zone of saturation.
• The growth of population may be conveniently represented by Logistic Curve. 
• The yield of underground source may be obtained by pumping and recupating test. 
• The water mains should be designed for 225% of the average daily water requirements.
• Turbidity of water is expressed in terms of silica scale.
• The maximum permissible color for the domestic supplies on paltinum cobalt scale is 10 -20 ppm.
• The maximum permissible turbidity for domestic supplies on silica scale is 5-10 ppm. 
• The maximum permissible chloride content should not exceed 250 ppm.
• Total solid content 500 ppm.
• Maximum Ph value of water will occur at 0.
• The most common causes of acidity is Carbon dioxide.

Methods of Forecasting population

The following methods are used to forcasting the population:

1) Arithmetical increase method

In this method, a constant increase in the growth of population is added periodically and the population at the required time is determined. This method is based on an assumption that population is increasing at constant rate. This method is most suitable for old cities and towns which are stabilised.

2) Geometric Increase Method

It is based on the assumption that the percentage increase in population from decade to decade or a constant interval of time remains constant. It is suitable for larger cities.

3) Incremental Increase Method

In this method, the average of increase in population is found out by arthimetical increase method and to this is added the averageof the net incremental increase once for every future decade.

4) Decreasing Growth of Rate

This method is similar to geometrical increase method except that a changing rate of decrease is assumed rather than a constant rate of increase. The changing rate of large and old cities is generally considered to be a decreasing rate.

5) Simple Graphical Method

In this method, plotting of population of a city for the last few decades to a suitable scale on the graph paper with respect to decade and then extending the curve so obtained smoothly to forecast the future population of various decades.