Water Uses and Consumption PDF

 Uses of water:  The uses of water in community are many, and the requirement in quality and quantity are varied.  The uses of water include:-  Domestic use  Public purposes  Industrial purpose  Agricultural purpose.  Power production  Carrying away waste  Water demand...

 Uses of water:  The uses of water in community are many, and the requirement in quality and quantity are varied.  The uses of water include:-  Domestic use  Public purposes  Industrial purpose  Agricultural purpose.  Power production  Carrying away waste  Water demand ; the demand of water may be broken into the following classes  1-domestic water demand  2-industrial water demand  3-demand for public use  4-fire demand  5-water required to compensate the losses in waste ,thefts etc.  For correct estimate of total water demand all the above demand should be considered.  1- domestic water demand:  This includes the water required in private building for cooking washing ,bathing ,gardening, sanitary purposes.  The domestic water demand depends upon the living condition of consumer  The total domestic water consumption may amount to 50 to 60% of the total water consumption.  Industrial water demand: This consumption includes water used in factories ,offices, hotels ,hospitals etc. This demand depend upon the nature of the city, number and types of industries. On an average ,20 to 25% of the total water demand may be allowed for this type of demand in the design. S.No Description Consumption of water per Head per day in litres 1. Bathing 55 2. Washing of clothes 20 3. Drinking 5 4. Cooking 5 5. Washing of Utensils 10 6. Washing of House 10 7. Flushing of W.C 30  Demand for public use:  Public demand includes the quantity of water required for public utility purposes, such as watering of public parks, gardening, sprinkling on road, use in public fountains etc.  In many water supply schemes these demands are not believed as essential and a nominal amount not exceeding 5% of the total demand is kept on an arbitrary basis.  Purpose Water requirements Public parks 1.5 litres/m2/day Street washing 1.0 – 1.5 litres/m2/ day Sewer 5.0 litres/ m2 /day  Fire demand:  It is the quantity of water required for fighting a fire outbreak.  For high value cities, water requirement for this purpose is particularly essential.  The quantity of water required for this purpose can be found out by applying certain empirical formulae.  The most common are:-  1- national board of underwriters formula:  Q = 1020 √ p (1 – 0.01 √p)  When converted into metric units then it is expressed as  Q= 64 √p (1 -0.01 √ p ) in litre per sec  2- free-man,s formula:-  p  Q = 1136.5 { ― + 10 }  10  Where Q =fire demand in US gallons per minute.  P = population in thousands  2- free-man,s formula:- p Q = 1136.5 { ― + 10 } 10 Where Q =fire demand in US gallons per minute. P = population in thousands  The previous high quantity of water for fire fighting is required few times in a year and that too short time of 4 to 5 hours only.  If this quantity is calculated on yearly basis ,it will be very small amount which will not much effect the total requirement.  The minimum pressure at fire hydrant should be 1 – 1.5 kg/sq.cm which should be available even after 4 to 5 hours of constantly using fire hydrant.  National board of fire underwriters requires provision for 5 hours fire flow in places of less than 2500 population and provision for 10 hours flow in larger places.  Example determine fire flow and storage required for fire protection in a city of 40,000 population according to the requirements of national board of fire underwriters?.  Solution. Refer table:  Required fire flow = 27000 litre/ minute for 10 hours.  fire flow to be provided by storage or by other means = 27000 ₓ60 ₓ10  = 1,62,00,000 litres  Water required to compensate losses in waste, theft:  This includes the quantity of water lost in leakage at the joints and fittings, stolen water due to unauthorized connections.  These losses can be reduced by providing good fittings proper inspection and investigation against water thefts.  This quantity is generally taken as 15% of total water consumption for a well managed water works.  The per capita demand It is annual average amount of daily water required by one person and includes the domestic, industrial, public use and the water lost in thefts and wastes. if Q = total quantity of water required by a city per year(in litre) p = population of the city Then per capita demand in litre per day =  Q  Per capita demand =  P×365   Factors affecting per capita demand:  The various factors which affect the per capita demand are:  1-climatic condition  2-size of city  3-habits of people  4-industries  5-cost of water  6-Qualityof water  7-pressures in distribution system  8-sewage facilities  9-system of supply  10- method of charging  population Consumption in litres per capita/day upto5000 90 5000 ---20,000 110 20,000---50,000 135 50,000------200,000 180 Over 200,000 200  Variation in rate of demand or consumption:  The per capita demand, which we have studied in the previous articles, is the average consumption of the year.  In practices it has been seen that this demand does not remain uniform throughout the year but it varies from season to season, even from hour to hour.  Variation in rate of demand or consumption:  The per capita demand, which we have studied in the previous articles, is the average consumption of the year.  In practices it has been seen that this demand does not remain uniform throughout the year but it varies from season to season, even from hour to hour.  Variation in rate of demand may be termed as  1-seasonal or monthly variation  2-daily variation  3-hourly variation  Seasonal variation:  In summer the water demand is maximum, because people will use more water in bathing cooling, lawn watering, street sprinkling.  This demand has been reduced in winter  This fluctuation may be up to 150% of the average annual consumption.  Daily variation:  The rate of demand for water may vary from day to day also.  This due to habits of consumer, climatic condition, holidays.  On the day of mass marriages or some fair, the rate of water demand will be more.  The maximum daily consumption may be much as 180% of the average annual consumption.  Hourly variation:  The rate of demand for water during 24 hours does not remain uniform and it varies according to hours of the day.  The maximum hourly consumption may rise up to 200% that of average daily demand.  Population present and future After deciding the quantity of water required by an individual, the next step in the design of water supply scheme will be to find the total quantity required by a community. Knowing the present population from the most recent census, it is possible to determine the present demand, but for the design what is required; is demand in future.  Generally population will be growing every year and hence there will be growing demand for water also.  The design period taken is generally 20 to 30 years. Methods of forecasting population The following are the methods used for population forecast: 1- arithmetical increase method:- In this method, the increase in population is assumed to be constant and an average increase of the last 4 to 5 decades is calculated and added in the present population to determine population of the next future decade.  The population can be found out at the end of n year or n decades.  Pn = p+ n x i  Where p =present population  I = yearly or per decade increase of population.  2- geometrical increase method :  In This method the average % age of growth of last few decades is determined, the forecasting is done on the basis that percentage increase per decade will be the same.  Thus the population at the end of n years of decades is given as : P n = p{ 1+ i } n  ----  100  Where i = yearly or per decade increase of population.  3- incremental increase method:  This method is an improvement over the arithmetical increase method.  The average increase in the population is calculated by the arithmetical method and to this is added the average of the net incremental increase once for each future decade.  The following data have been obtained from the census department regarding population of X town:-  Year 1960 1970 1980 1990  population 12,000 17,000 22,000 28,000  Calculate the probable population in the year 2000 , 2010, and 2020.  Solution : the average increase in population after every decade  ⅓ (5000 + 5500 +6000)  =5500 persons.  The probable population in various decades will be calculated by the formula. P n = p + n x I  Year probable population  2000 28500+1 x5500 = 34,000  2020 28500 +3x 5500 = 45,000  4- changing rate of increase :-  It is similar to the geometrical increase method except that a changing rate rather than a constant rate of increase is assumed.  The changing rate for large and grown up cities is usually considered to be a decreasing rate.  This method gives quite rational result.  5- Graphical method :-  In this method the population of last few decades is correctly plotted to the scale on the graph paper.  The curve is smoothly to find the future population.  Sometimes population trend lines are plotted similar expected population trend lines are drawn. 6 comparative methods:-  Cities having similar characteristics to the city whose population is to be estimated are selected.  The on the basis of those cities , the population of the required city is forecasted.  Graph maybe plotted if necessary. Total quantity of water for a town :- As we have discussed above that the water supply project is require for domestic, industrial, trade purposes etc. For estimating the total quantity of water required by a town , the water used for various purposes should be added and 30 to 40 % wastage allowance is also given. But this total requirement will vary from town to town which will depend so many factors.  Climatic conditions  Habits of people  Industry  Cost of water