1. Week 5: Water Demand WATER SUPPLY ENGINEERING EAT 237
Fahmi Muhammad Ridwan
SCHOOL OF ENVIRONMENTAL ENGINEERING
UNIVERSITI MALAYSIA PERLIS
2014

2. Lecture Outline:
Water Use/Consumption Initial & Design Years (or Design Period) Population Projection Per capita Water Demand Water Demand Estimation Fluctuations in Water Demand

3. DOMESTIC USE Almost 30 - 60% of total water supply is for domestic use
In-house use  for drinking, cooking, bathing, ablution, sanitation, house cleaning, laundry and car washing
Out-of-house use  for garden watering, lawn sprinkling and bathing pools
In other countries, average water consumption for domestic use is between L/person/day
In Malaysia, it is generally 225 L/person/day

4. DOMESTIC USE
Factors affecting average water consumption for domestic use:
Climate
Social status
Water quality
Cost of water supply
Sanitation system
Supply system
Water pressure

5. COMMERCIAL USE Includes water consumption in commercial establishments
 motels, restaurants, offices, hotels, office buildings, shopping centres, service stations, movie houses, airports
About 10-20% of total water demand
Water demand depends on:
Type and area of commercial establishments
Number of commercial establishments
Number of workers or residents

6. WATER/PRODUCT (MASS RATIO)
INDUSTRIAL USE
Generally, large industries develop their own water supply systems
Normally, only small industries purchase water at about 25-35% of total water demand
Some industrial water demand data:
PRODUCT
WATER/PRODUCT (MASS RATIO)
Cotton, Fur
Steel, Wood, Pulp, Paper
10-300
Slaughtering and Packaging
15-25
Petroleum production
3-10
Milk, dairy
3-35

7. INDUSTRIAL USE Industrial water demand may be estimated based on:
Type of industries
Size of organisation
Water quantity and quality
Cost of water supply

8. AGRICULTURAL USE
Treated water is also used for crops, livestock, horticulture, greenhouses, dairies and farmsteads
In Malaysia, irrigation is predominately for paddy cultivation and to a minor extent for vegetables and cash crops.
Agriculture will remain the main user of water in the future, however, its importance will decline with growth in industrial sectors

9. *3 principal water-using sectors in Malaysia
AGRICULTURAL USE
*3 principal water-using sectors in Malaysia

10. AGRICULTURAL USE

11. PUBLIC USE Water used for
public buildings (e.g. city halls, jails, schools)
public services (e.g. street watering/washing, public parks irrigation, sewer flushing, fire-fighting)
Account for 5-10% of total municipal water demand
During dry seasons, sometimes water from public drains is used to reduce demand for treated water supply

12. LOSSES (UWF)
In a water supply system, a certain amount of water is lost or unaccounted for because of:
meter and pump slippage
leaks in mains
faulty meters
water evaporation
fire-fighting
unauthorized water connections
In municipal supply system, it is usually about 8-18% of total demand
In Malaysia, it is between 17-57%

13. Total water demand Total water demand can be divided into:
Domestic use: 45-55%
Industrial and commercial use: 15-20%
Public use: %
Leakage and losses: 15-20%
Fire-fighting: < 1%

14. Initial & Design years
A water treatment plant is generally designed and constructed to serve the needs of a community for a number of years in the future
Normally designed not > 50 yrs, mostly between yrs
Initial year  the year when the construction is completed and initial operation begins
Design year/period the year when the facility is expected to reach its full designed capacity and further expansion may be necessary

15. Determination of design years
Period of design years depends on:
Useful life of treatment units (includes wear, tear, development in water treatment technology and process)
Convenience of future expansion
Anticipated changes in drinking water quality requirement
Anticipated changes in raw water quality
Growth pattern of the community and the service area
Performance of treatment facility during early years when it is oversized
Interest rate, cost of present and future construction, and availability of funds

16. Determination of design years
STRUCTURAL COMPONENT
CHARACTERISTICS
DESIGN YEAR (YEAR)
Dam, water conduit, water tunnel and reservoir
Complicated and expensive for future expansion
25 – 50
Water treatment works
Susceptible for future improvement
10 – 25
Distribution system
Life is very long and replacement is expensive
Indefinite period
Capacity designed is based on maximum anticipated development of the area served

17. The importance of design years in water supply scheme
Avoid water supply scheme design become uneconomic due to large and expensive structures (i.e. pump, treatment units and water mains) have to be replaced within a brief period
Avoid from having difficulties to replace distribution system elements which were normally laid below the main streets without adversely affect the surrounding, such as distracting traffic movement
Ensure overall cost of water supply scheme development is bearable (avoid overestimation which can burden a relatively small community with the cost of works designed for larger population)

18. POPULATION ESTIMATION
Data of previous and current population can be obtained from population and housing census done by Dept of Statistics
Factors affecting population growth?
Birth rate
Death rate (Mortality)
Migration
Several methods are used to estimate population growth Arithmetic; Geometric; Incremental Increase; Decreasing Rate of Increase; Graphical Comparison; Ratio and Correlation

19. ARITHMETIC PROGRESSION
Population is assumed to increase at a constant rate
Commonly used for short term estimates (1-5 years) only
Can be used for big/old city which is almost fully developed
Pn = Pi + nI
Pn = number of population in year n
Pi = number of current population
n = number of year per decade
I = average population growth rate per decade

20. GEOMETRIC PROGRESSION
Population is assumed to increase in proportion to the number of population present
Based on percentage of population increment between decades
Suitable for rapidly developing cities
Pn = Pi (1 + i/100)n
i = average percentage of population growth per decade

21. INCREMENTAL INCREASE Pn = Pi + n(I + m)
Combination of arithmetic and geometric method
m = average increment growth per decade
Pn = Pi + n(I + m)

22. DECREASING RATE OF INCREASE
Population is assumed to reach some limiting value or saturation point
Suitable for developed cities
Pn = Pi 1 + i – k n
100
k = average decreasing rate of increase per decade

23. Per capita demand
Per capita demand  Average daily amount of water required per person during a period of 1 year, and including all treated water that is used by residential, commercial, industrial, public service and system losses
Estimated by dividing the annual average daily water consumption by total population served
Unit  liter/capita/day (LPCD)
Per capita demand = total water consumption (Q)
total population (P) x 365

24. Category of per capita demand
The value of per capita demand is categorised to:
City (number of residents > people)
230 – 320 L/person/day
Small town
180 – 230 L/person/day
Rural area
135 – 180 L/person/day

25. Water Demand Estimation
WDn = (Pn x C x F) + Da
WDn = total water demand at the end of year n
Pn = projected population at the end of year n
C = per capita consumption at the end of year n
F = service factor at the end of year n
Da = additional demand at the end of year n

26. Water demand estimation
Service factor  represent percentage of population that will receive water supply service
0.8 service factor  means distribution system reaches 80% of population
Additional demand includes water demand for industry, institutional etc

27. Additional Demand Estimation
Industrial Demand
Water Demand = area of industry x volume of water consumed
Heavy industry
Normal consumption: L/ha/day
Water Demand = area of industry x
Light industry
Normal consumption: L/ha/day
Water Demand = area of industry x

28. Fluctuations in water demand
Water demand for a city changes within years, months, weeks, days, hours and from one season to another
General changes in municipal water demand
Changes from dry season (hot days) to rainy season (wet days)
Water demand will be reduced
Daily changes
During weekends and public holidays, water demand for domestic use will be high, while demands for commercial and industrial uses are low
Within a day, there are 2 demand peaks  morning and evening

29. Fluctuations in water demand
Fluctuations in water demand influence the design of various component in a water supply scheme
Generally
Monthly fluctuation is used for design of dam and storage tank
Daily and hourly fluctuations are used for design of pumping system, service tank, water mains etc

31. Influence of Fluctuations to Water Flow Estimation
Average annual demand are not sufficient for design of water systems due to water demand fluctuations
Pumping records or flow measured at pumping station/water source can be used for evaluation of variations in demand
In absence of these data, maximum flow rates may be used for estimation
Max daily consumption normally ~ 180% of annual average demand

32. Goodrich Formula (peak flow factor)
Based on moderate-sized residential
P = 180t -0.1
P = percentage of annual average day demand for period t
t = length of the period in days
Max daily demand = 180% of annual average
Max weekly demand = 148% of annual average
Max monthly demand = 128% of annual average
Max hourly demand (peak hour rate) = 150% of max daily demand

33. Max day demand
Max day demand  amount of water required during the day of maximum consumption on any 24-hour operating day of the year
Used to determine maximum or peak flow rate in a water supply system
Sensitive to weather conditions
Ratio of maximum day demand/average day = 1.6 – 2.2
Typically 1.8 (peak flow factor)

34. Peak hour demand
Peak hour demand  amount of water required during maximum consumption hour in a given day
Used to analyze peak capacity required of the distribution system, elevated reservoirs, and service pump to be able to deliver water during the peak hour of the day
Peak hour demand/max hour demand = 1 – 2
Typically 1.5 (peak flow factor)

35. Fire demand (Undue demand)
Based on moderate-sized residential
F = 18C(A)0.5
F = required flow in gal/min (L/min  3.78)
C = coefficient related to the type of construction
A = total floor area in ft (m2 x 10.76) excluding basement
C = 1.5 for wood construction
= 1.0 for ordinary construction
= 0.8 for noncombustible construction
= 0.6 for fire resistive construction

36. Influence of flow fluctuations to design capacity
Flow required during max day demand, QMD demand
= Max day demand factor x flow required for annual average daily demand (QAAD demand)
Can be used for design of water treatment plant
Flow required at peak hour demand, QPH demand
= Peak hour demand factor x flow required for max day demand (QMD demand)
Can be used for design of water distribution system (pumping, service tank, water mains)

37. Influence of flow fluctuations to design capacity
Flow required based on fire flow
Qfire = 3.86P(1-0.01P)
Qfire = fire flow, m3/min
P = population in 1000
Flow required at peak hour (to design capacity of water distribution system)
QMD demand + Qfire @ QPH demand (choose higher flow)