Water Demands

 WATER DEMAND 

◇Water demand is defined as the volume of water requested by users to satisfy their needs.

◇ Types of water demands

1. Domestic water demand~ This includes the water required in residential building for drinking ,cooking, bathing, etc .As per IS:1172-1993, the minimum domestic consumption for a town with full flushing system should be taken at 200 litre per head per day although it can be reduced to 135 litre per head per day for weaker section and LIG colony depending on upon prevailing condition.

2. Industrial water demand~ It represents the water demand of industry which are either existing or likely to be started in future in the city for which water supply is being planned. This quantity will thus vary with the number and types of industry present in the city. The ordinary per capita consumption on the account of industrial need of a city is generally taken as 50 litre per person per day.

3. Institutional and commercial water demand~The water requirement of Institutions should also be assessed and provided for, in addition to domestic and industrial water demand ,discussed above. On the average ,a per capita demand of 20 litre per head per day is considered to be enough but this demand may be as high as 50 litre per head per day for highly commercialized cities.

4.Demand for public uses~ It includes the quantity of water required for watering of public parks, gardening ,washing and sprinkling on road etc.Only 10 litre per head per day is added in this category.

5. Water required to compensate losses in theft and wastes~This includes the water lost in leakage ,stolen water. These losses should be taken into account while estimating the total requirements.

6.Fire demand~The rate at which water is required for fire fighting is very large, the total amount of water consumption hardly amounts to 1 litre per head per day .The per capital fire demand is thus generally ignored while computing the total per capital water requirement of a city.

◇Rate of demand (Per capita) is the annual average amount of daily water required by the one person and includes the domestic use, Industrial and commercial use ,public use etc.

◇ Factor affecting per capita demand

1.Size of the city~The per capita demands for Big City is generally large as compared to that of smaller towns.

2.Climatic conditions ~At hotter and dry dry place,more bathing ,cleaning and air cooling is required so more water is demanded.At extremely cold country more water is demanded because people may keep their tapes open to avoid freezing of Pipe and more leakage from pipe joints ,since metal contract with cold.

3.Types of gentry and habit of people~ In this condition water demand is directly proportional to economic status of the consumers.

4. Industrial and commercial activities~It increase the water consumption by large amount.

5. Quality of water supplies~ If test and quality of water is good than more water is demanded.

6. Pressure in the distribution system~If the pressure in the pipe is higher and sufficient to make the water reach at third or fourth floor then Water consumption is more.

7. Development of Sewerage  facilities ~More in the flush system and less in old conservation system of latrine in adopted

8. System of supply

9. Cost of water

10. Policy of metering and method of charging

◇ variations in demand

~ There are wide variation in the use of water in the different season ,in different month of the year, in different days of the month and in different hours of the days.Seasonal or monthly variation are well known in tropical countries like India where the rate of consumption reaches maximum in summer season and rate of consumption goes down in winter months

~Seasonal variation occur due to large use of water in summer season lesser used in winter and much less in rainy season .

~Monthly variation: In this rate of demand of water varies considerably from month to month .

~Daily variation: In this rate of demand of water varies from day to day; this is due to change in the day to day climatic condition or due to the day being a holiday or some festival day. 

~Hourly variation: The demand of water also varies from hour to hour of the day.

◇Goodrich formula:

◇ Design period is the number of years in the future for which the purposed facility would meet the demand of the communities.

◇ Factors affecting the design periods

1.Useful life of component structure and the chances of their becoming old and obsolete .

2.Ease and difficulty that is likely to be faced in expansion in future.

3. Amount and availability of additional investment likely to be incurred of additional provisions.

4. The rate of interest on the borrowing and the additional money invested .

5.Anticipated rate of population growth including possible shifts in industries ,commercial establishments.

◇ Population data and Population growth

~The present population of a town can be best determined by conducting an official enumeration called census .

~The Government of every country generally carried this officially survey at interval of 10 year called the decennial census .

~All this data is given to planner of water supply schemes that the data is then used for predicting the future population of the city at the end of design period.

~ Factor affecting population growth

1. birth rate 

2. death rate 

3.migration 

and also the other factors that affect population growth is war, disaster etc.

~ Ideal population growth curve :When all these factor do not produce extra ordinary changes the population would probably follow the growth curve characteristic of living things within Limited space or economic opportunity. The curve is S shaped and known as Logistic Curve.

◇ Population forecasting is defined as the method of determining the expected population for a particular design period of a water supply system with the help of the study and analysis of future event and available records.

◇ Arithmetic increase method: This method is based on the assumption that the population is increasing at constant rate that is dP / dT is constant.

◇ Geometric increase method: In this method the per decade percentage increase is assumed to be constant and the increase is compounded over the existing population every decade. This method is also known as uniform increase method.

◇ Method of varying increment or incremental increase method :In this method the per decade growth rate is not assumed to be constant as in Arithmetic or geometric progression method but is progressively increased or decreased ,depending upon whether the average of incremental increase in the past data is positive or negative.

◇ Decreasing rate of growth method :In this method the average decrease in the percentage increases is worked out and in then subtracted from the latest percentage increase from each successive decade

◇ The Logistic Curve method:In normal condition the population of city shall grow as per Logistic Curve .Verhulst has put forward a mathematical solution for this Logistic Curve .

◇simple graphical method: In this method the graph is plotted from the available data between time and population .The curve is then is smoothly extended up to decide year. 

◇comparative graphical method :In this method the cities having condition and characteristics similar to the city whose future population is to be estimated our first of all selected .It is then assume that the city under consideration will develop as the selected similar Cities have developed in the past. 

◇ The ratio method The apportionment method:In this method of forecasting future population of city,the city's census population record is expressed as a percentage of population of the whole country.