1. Water Demand Management (WDM)
Lectures 3,4

2. Water Demand Management (WDM)
Water Demand management aims at achieving desirable demands and desirable uses. It influences demand in order to use a scarce resource efficiently and sustainably.
WDM is not necessarily the same as decreasing water demand; in certain situations managing the demand may mean to stimulate the demand that had been suppressed, here we have to improve water services and increase water consumption
WDM uses technical, legal and economic incentives in combination with awareness raising and education; in order to achieve more desirable consumption patterns, both in terms of distribution between sectors and quantities consumed, coupled with an increased reliability of supply.
WDM is always concerned with increasing the efficient use of water. Minimizing leakages is often the most cost-effective strategy towards system's improvement.

3. Water Demand Management
Goals of demand-side management of water
Increased efficiency of water use
Safeguard the right of access to water for future generations
Improve allocation among competing users
Decreased need for large investments in infrastructure (like dams, Desalination Plants)
More cost effective water use
Changes to the nature of water demand and the way people use water

4. WDM Tools / Instruments
Technical / regulatory tools
Reduction of water losses
Leak detection and repair
Inspection of illegal connections
Modern irrigation techniques
More crop for drop
Improved O&M
Metering
Rationing
Cropping patterns
Timing and regulations of outdoor irrigation
Dual distribution system
Good quality for drinking and cooking
Lower quality for other uses
Internal recycling
Water savings appliances/devices
Automatic taps
Spray showers
Dual flush system
Rainwater harvesting / promote reclaimed WW (supply side)

5. WDM Tools / Instruments
Social tools
Behavioral changes
Public awareness
Education curricula
Economic tools
Water pricing
Increasing block tariff
Implementation incentives
Subsidies
Taxes
Loans
Promotions for compliance
Fines / penalties / fees
Legal tools
Policies / laws
Regulatory framework

6. Global Water Resources

7. Global Water Resources

8. River Basin Water Balance

9. Water Demand – Municipal &Industrial (M&I)
Factors:
Population and population density
Housing type and standard of living
Sanitation type
Climate conditions
Economic conditions and income level
Water availability – Rationing
Water quality
Pricing policies and tariff structure

10. Per - Capita Demand Basic Human Needs
WHO (guidelines for small communities)
Average 150 l/c/d
Minimum 100 l/c/d

11. Per - Capita Demand
150 l/c/d
300 l/c/d
420 l/c/d
165 l/c/d

12. Per - Capita Demand

13. 1- WHO guidelines for water supply systems in small communities
الاحتياجات الفردية
المنزلي ( الاستعمال داخل المنزل )1
الحد الادنى =100 لتر للفرد في اليوم
المتوسط = 150 لتر للفرد في اليوم
الخدمات العامة ( يشمل متطلبات المساحات الخضراء و الدفاع المدني )
تقدر بحوالي 5% من الاجمالي
الصناعي
من 7% حاليا الى 14% في 2020
* أقل من 15% من مصادر مياه الشرب تعتبر مطابقة للمواصفات المحلية
1- WHO guidelines for water supply systems in small communities

14. * Based on PCBS including the returnees before 2000
الإحتياجات الإجمالية
WSSPS, 2000 *
* Based on PCBS including the returnees before 2000

15. Population Growth rate: Similar to Water Balance
dP/dt = change in population during time step (capita)
B = number of birth per unit of time (capita/year):
D = number of death per unit of time (capita/year)
I = immigration (capita/year)
O = emigration (capita/year)
L= life expectancy (year)
Similar to
Water Balance
b is the birth rate which the amount of children born per person during his/her life
d is the death rate
d = 1 : steady state situation
d < 1 : population is growing where more young people than old people.
d > 1 : more elder people than young people ( case of china b=0.5) where b < 1.

16. Population Ignoring immigration and emigration
1- if (b-d)> 0: more children are born than die
2- b=d: the population is constant.
The exponential growth model can also be written as:
Other models: Linear Model:

17. Population Example: Number of children 4 r=(4-2)/60=0.033

18. Population
Other models: Saturation model P Ps t

19. Gaza Population

20. Population Pyramid

21. Irrigation Water Demand
ETo: Reference evapotranspiration: The evapotranspiration rate from a reference surface, not short of water. The reference surface is a hypothetical grass reference crop with specific characteristics

22. Single Crop Coefficient - Kc
Case A: Pan placed in short green cropped area
Case B: Pan placed in dry fallow area
RH mean
(%)
low
< 40
Medium
High
> 70
medium
high
Wind
speed
(m s-1)
Windward side
distance of
Green crop (m)
distance of dry
fallow (m)
Light 1
.55
.65
.75 .7 .8
.85
< 2 10 .6
100
1000 .5
Moderate
.75.
2-5
.45
.6.
Strong
5-8 .4
Very strong
> 8
.35

25. Factors Influencing Kc
Crop height: The crop height influences the aerodynamic resistance term (ra) of the FAO Penman-Monteith equation and the turbulent transfer of vapour from the crop into the atmosphere.
Albedo (reflectance) of the crop-soil surface. The albedo is affected by the fraction of ground covered by vegetation and by the soil surface wetness. The albedo of the crop-soil surface influences the net radiation of the surface, Rn, which is the primary source of the energy exchange for the evaporation process
Canopy resistance: The resistance of crop to vapour transfer is affected by leaf area (number of stomata), leaf age and condition, and the degree of stomatal control. The canopy resistance influences the surface resistance, rs
Evaporation from soil, especially exposed soil.
Initial stage
Crop development stage
Mid-season stage
Late season stage

26. Estimation of ET0 Penman-Monteith Method
ETo reference evapotranspiration [mm day-1],
Rn net radiation at the crop surface [MJ m-2 day-1],
G soil heat flux density [MJ m-2 day-1],
T mean daily air temperature at 2 m height [°C],
u2 wind speed at 2 m height [m s-1],
es saturation vapour pressure [kPa],
ea actual vapour pressure [kPa],
es - ea saturation vapour pressure deficit [kPa],
D slope vapour pressure curve [kPa °C-1],
γ psychrometric constant [kPa °C-1].

27. Tedious Calculations
G ???
Rn ???

31. Epan Method ETo = Kp Epan ETo reference evapotranspiration [mm/day]
Kp pan coefficient [-]
Epan pan evaporation [mm/day].

32. Effective Rainfall (USDAS-SCS Method)
f = correction factor depends on average net application depth
or soil moisture depletion before each irrigation 
P = the gross monthly rainfall in mm
ET0 = the monthly reference evapotranspiration

33. Gaza Example

34. Gaza Example

35. Gaza Example Crop Category Crop Type Citrus
Orange / lemon / grapefruit
Fruit trees
Apples / pears / peaches / apricots / almonds
Vegetables1
Cucumber / squash / cabbage
Vegetables2
Tomato / sweet peppers / egg plants / potato
Field crops
Wheat / barley
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Citrus
0.7
0.65
Fruit trees
0.9
0.4
Vegetables1
1.15
0.95
0.6 1
0.75
Vegetables2
0.8
Field crops
0.3

36. Gaza Example

37. Gaza Example

38. Gaza Example

39. Gaza Example

40. Gaza Example

41. Demand-Resources Gap

42. Other Water Demands Environmental Demand Hydropower
Environmental flow: the quantity and quality of water required to sustain aquatic ecosystems and the ecological components, processes and functions on which people depend
Ecological functions of flow
Extreme low (drought) flows
Population regulation; life history cues
Low (base) flows
Provide habitat for aquatic biota, maintain water temperature and water chemistry, provide drinking water for terrestrial animals
High flows
Shape river channel, prevent encroachment of riparian vegetation, flush sediments and pollutants, maintain estuaries and floodplain
Hydropower
Power generation requirements
E = P T = et eg ρ g Q H T

43. Water Pricing
Dublin and Rio conferences, Agenda 21: Water should be managed as an economic good, provided water for drinking purposes and other basic needs are made available at prices that are widely affordable locally

44. Water Pricing make a key instrument for the implementation of Demand Management:
Increased price reduces the demand;
Increased price increases supply (firstly, because marginal projects may become affordable and secondly because it becomes attractive to reduce losses);
increased prices facilitate reallocation among sectors;
Increased prices improve managerial efficiency.

45. Cost of Water Water pricing should have two purposes:
to recover costs
to enhance water use efficiency
External costs (economic externalities): environmental damage, pollution, effect on downstream users and health hazards
The economic price should also reflect the scarcity of the resource, which is generally expressed in the opportunity cost (the cost of not being able to use the resource for another social or economic activity).

46. The following questions to be answered:
How should we determine the full social cost with respect to long-term marginal social costs and external environmental cost?
How should we identify users (consumptive users, non-consumptive users and polluters) to which costs should be charged?

47. Goodman (1984) stated that :
The economic value of a product or service from a water resources is estimated as the amount of users are willing to pay for it.
This is not entirely true since water is essential to life and there is no alternative for it .
The variation of the willingness to pay can be conceptually shown by the curve of price per demand.

48. Price vs. Demand Q where Q is the quantity of demand for the good
Assumptions:
constant incomes
constant preferences (willingness to pay or economic value of the water)
where
Q is the quantity of demand for the good
P is the price of the good
c is a constant
E is the elasticity of demand (-1 , 0) (the slope of the curve)
Price
Type of use

49. Price vs. Demand

50. Price vs. Demand

51. Elasticity of Demand
If E ≤-1, the response to a price increase is said to be elastic or reactive.
If -1<E, the response to a price increase is said to be inelastic or rigid.
Essential needs
More rigid
No alternatives
industry and agriculture
More elastic
Alternatives available

52. Elasticity of Demand Example (1): Example (2):
What is E if the a price increase by 100% (P1=2*P0) resulted in a 20% decrease in water use (Q1=0.8Q0)?
dP/P = (P1-P0)/P0 = (2P0-P0)/P0 = 1
dQ/Q = (Q1-Q0)/Q0 = (0.8Q0 -Q0)/Q0 = -0.20
E = -0.20/1= (rigid)
Example (2):
What is E if the price is increased by 10% and a decrease of the consumption of 5%?
dP/P = 0.1
dQ/Q = -0.05
E = -0.05/0.1= (rigid)

53. Elasticity of Demand Concluding:
the elasticity of water consumption is generally low.
the price elasticity is greater when the price is higher.
in the household sector, the price elasticity varies between and
with respect to drinking water the demand-price relation will never be elastic (E < -1)
in the industrial sector, the majority of estimates are in the range of to

54. Example: Does increasing price result in increasing revenues?
Revenues or the amount of money people are willing to pay = QP
If we compute the relative change in the revenue :
(1+E)>0 , an increase of the price results in an increase of a revenue

55. Elasticity, water use and climate types
The availability of alternative of water
rigid
elastic E
Go to 8-SMetaxas.pdf file

56. Increasing Block Tariff
Considerations
Cost recovery
Equity (access to basic needs)
Block purpose:
Cross-subsidy from rich to poor users
Compromise between full cost recovery and equity

57. Increasing Block Tariff Example
the poorest households have access to a lifeline amount of water and do not spend more than a certain percentage of their income on water
subsidized
Block2:
ideal’ per capita water consumption level
ensure “well-being” e.g. twice the lifeline amount
charged at the full cost of water supply for the amount above block1
some subsidy
Block 3:
above the well-being amount but less than a certain upper limit (e.g. 4 times the lifeline amount)
Charged at full cost of water over their entire use
Block 4:
water use above the amount specified in the third block will be charged at a rate that will off-set the subsidy received by households falling within blocks 1 and 2

58. Increasing Block Tariff Example

59. Increasing Block Tariff South Africa Example