4 Water Consumption & Water Demand

WATER CONSUMPTIONAND

WATER DEMAND• Average Day Demand• Maximum Day Demand• Maximum Hour Demand• Water Supply Fixture Unit

2015 PLUMBING REVIEW 004

Water Consumption vs. Water Demand

• Water Consumption is the amount of water consumed by all residents, institutions, etc. when provided with water service facilities.

• Water Demand is the sum of water consumption and unaccounted for water*.

• Unaccounted for water –the amount of water losses thru leakages and pilferages

Danilo V. Ravina New NAMPAP Cebu Chapter

Danilo V. Ravina New NAMPAP Cebu Chapter

Water Demand

• Knowledge of the quantity of water needed to satisfy the requirement of the building or community is necessary in the design of any water supply system.

Danilo V. Ravina New NAMPAP Cebu Chapter

Water Consumption

• Oftentimes, water is utilized mainly for domestic consumption which is affected by:

1. Size of population served.

2. Standard of living of the consumers

3. Quality and quantity of water available

4. Cost of water to consumers

5. Habits and manner of usage of the consumers

6. Climate7. Livestock, poultry, hogs

and other animals being raised by the residents

8. Plants and gardens being maintained by the residents

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Estimated Water Consumption

Use Consumption in liters/capita/day

Rural Area 1. Public Faucet 60 2. Individual Household Connection

100

3. Combined Public Faucets & some Household Connection

80

Suburban Area 120

Urban Area 150

Average Human Water ConsumptionUse % 120 liter

Consumption150 liter Consumption

Kitchen 15% 18 liters 22.50 liters

Drinking 5% 6 7.50

Shower 10% 12 15

Laundry 20% 24 30

Toilet Flush 40% 48 60

Others: Carwash, Water gardens

10% 12 15

TOTAL 100% 120 liters 150 liters

Breakdown of Water Usage(per capita/day)

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Building Type Consumption in liters/capita/day

Airports (per Passenger) 11 -19

Apartments (per resident) 151

Boardinghouses (per boarder) 150 – 189

Factories (per person/shift) 57 - 132

Hotels with T & B (twin sharing) 227

Hotels w/o T & B (per person) 189

Hospitals (per bed) 946 - 1514

Institutional Building (per person)

284 - 473

Large Residential Houses (per resident)

189 - 284

Building Type Consumption in liters/capita/day

Restaurants

• with toilets (per patron) 26 - 38

• without toilets (per patron) 9 - 11

• with bar / cocktail (add’l) 8

Schools (per student)

• with gym, canteen, shower 95

• with canteen only 76

• w/o gym, canteen, shower 57

Auditorium (per seat) 19

Stores (per toilet room) 151

Office (per person/shift) 57

Other Water Usage According to the Type of Building

Danilo V. Ravina New NAMPAP Cebu Chapter

Animal Consumption in liters/day

Each Milk Cow 133

Each Steer or Dry Cow 45

Each Horse 45

Each Hog 15

Each Sheep 8

Each 100 Chickens 15

Average Daily Livestock Consumption

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Leakages and Pilferages

• In addition to domestic consumption, allowance should be made for leakages and pilferages.

• Ideally, this should not be more than 15% of the total water sent to the distribution system.

Danilo V. Ravina New NAMPAP Cebu Chapter

Design Criteria

• The objectives of the design criteria are to establish goals such that if the criteria are met, consumers will receive water at reasonable quantities and cost.

• However, during the planning process, it may be necessary to modify the criteria to accommodate special requirements of the locality.

• Design criteria include:1. Design population2. Design period (when

applicable)3. Demand factors

a. Average Day Demandb. Maximum Day Demandc. Maximum Hour (Peak Hour) Demand

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Design Population

• Design Population is the number of individuals of the building or area to be served within the design period.

• The design population is equal to the present population multiplied by 1.15.

• Stated mathematically:Pp = 1.15 x P

where:

Pp = Projected population at the end of the design period

P = Present population

Based on 3% annual increase of population for the design period of 5 years: (0.03 x 5 = 0.15)

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Design Period

• The effective life of the project is dependent upon the size and source of the water supply, the life span of pumps, pipelines, and storage tanks. This may also include the availability of funds to finance the project

• The design periods recommended for the following appurtenances are:1. Pumps : 5 years*2. Wells, pipelines: 5 years *3. Storage Tanks: 5 years*

* The life of the system may last up to 20 years

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Demand Factor: Average Day Demand

• Average Day Demand is the sum of the daily water demands in one year divided by the number of days of that year.

• The Formula is: Average Day Demand = Design Population x Water Consumption Rate

• Use the value in Average Day Demand in the design of the Reservoir or Storage Tank capacity.

Demand Factor: Maximum Day Demand

• Maximum Day Demand is the day with the highest water demand. Usually, this occurs during dry season generally on a Monday.

• The formula is:

Maximum Day Demand = 1.30 x Average Day Demand

• The value from the Maximum Day Demand is used in determining the minimum pump capacity. (Except in Hydropneumatic Pressure System)

Danilo V. Ravina New NAMPAP Cebu Chapter

Danilo V. Ravina New NAMPAP Cebu Chapter

• Maximum Hour Demand or Peak Hour Demand is any hour of the day when the water demand is at its maximum. In most places this occurs early morning at 7 or 8.

• The formula isIf the Design Population is less than 600 persons:

MHD = (3 x Average Day Demand) ÷ Time*If the Design Population is more than 600 persons:

MHD = (2.5 x Average Day Demand) ÷ Time*

Demand Factor: Maximum Hour Demand

*Time = Duration of Usage

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• Maximum Hour Demand is used in:1. Estimating the diameter of transmission and distribution mains.

2. Estimating the minimum pump capacity in Hydropneumatic Pressure System.

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Example: Proposed 10 Storey Office Building

Determine the: 1. Average Day Demand2. Maximum Day Demand3. Maximum Hour Demand

Total Useable Floor Area: 10,000 square meters

Solve for:1. Capacity of Overhead Storage Tank, if the Gravity System is to be used.2. Capacity of Transfer Pump3. Capacity of Booster Pump and Pressure Tank, if the Hydropneumatic

Pressure System is to be used.

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Sample Calculations: Office Building

1. Design PopulationIf the population is not given or known, determine the gross floor area of the building and use the occupant load of 11 square meters per person.

2. Daily Water ConsumptionUse 75 liters/person/shift/day.

3. Duration of UsageUse 9 hours or 540 minutes of usage per day.

4. Maximum Hour DemandUse: (3 x Ave. Day Demand)÷Time, if the population is less than 600.Use: ( 2.5 x Ave. Day Demand)÷Time, if the population is more than 600.

Step 1. Solving for the Design Population (Pp).Pp = 1.15 (10,000m² ÷ 11m²/person)Pp = 1046 person

Step 2. Solving for Average Day Demand (AVD).AVD = 1046 person x lpdAVD = 78,450 liters/day

Step 3. Solving for Maximum Day Demand (MDD).MDD = 1.3 x Average Day Demand

= 1.3 x 78,450 litersMDD = 101,985 liters/day

Step 4. Solving for Maximum Hour Demand (MHD).MHD = (2.5 x Ave. Day Demand)÷Time

= (2.5 x 78,450 liters)÷540 minMHD = 363.19 liters/minute

Danilo V. Ravina New NAMPAP Cebu Chapter

Danilo V. Ravina New NAMPAP Cebu Chapter

Summary

• Average Day Demand:78,450 liters/day

• Maximum Day Demand: 101,985 liters/day

• Maximum Hour demand: 363.19 liters/minute

or 6.05 liters/second

Type of Fixture

Number of Water Supply Fixture Units

(WSFU)

Private Use Public Use

Bar Sink 1 2

Bathtub (with or without Shower over)

2 4

Bidet 2 4

Drinking Fountain (each faucet) 1 2

Hose Bibb 3 5

Laundry Tub or Clothes Washer 2 4

Lavatory 1 2

Shower (each head) 2 4

Sink (kitchen) or dishwasher 2 4

Urinal (wall or stall type) - 5

Water Closet – Flush Tank 3 5

Water Closet – Flush Valve: 19mm

3 6

Water Closet – Flush Valve: 25mm

6 10

Equivalent WATER SUPPLY FIXTURE UNITS (WSFU)

SUPPLY SYSTEMS PREDOMINANTLY FOR FLUSH TANKS

LOAD IN WATER SUPPLY FIXTURE UNITS (WSFU)

WATER DEMAND LOAD IN WATER SUPPLY FIXTURE UNITS (WSFU)

WATER DEMAND

Gallon per minute

Liter per second

Gallon per minute

Liter per second

1 3.0 0.19 60 32.0 2.02

2 5.0 0.32 70 35.0 2.21

3 6.5 0.41 80 38.0 2.40

4 8.0 0.51 90 41.0 2.59

5 9.4 0.59 100 43.5 2.74

6 10.7 0.68 120 48.0 3.03

7 11.8 0.74 140 52.5 3.31

8 12.8 0.81 160 57.0 3.60

9 13.7 0.86 180 61.0 3.85

10 14.6 0.92 200 65.0 4.10

12 16.0 1.01 250 75.0 4.73

14 17.0 1.07 300 85.0 5.36

16 18.0 1.14 400 105.0 6.62

18 18.8 1.19 500 124.0 7.82

20 19.6 1.24 750 170.0 10.73

25 21.5 1.36 1000 208.0 13.12

30 23.3 1.47 1250 239.0 15.08

35 24.9 1.57 1500 269.0 16.97

40 26.3 1.66 2000 325.0 20.50

45 27.7 1.76 2500 380.0 23.97

50 29.1 1.84 3000 433.0 27.32

ESTIMATING WATER DEMAND

ESTIMATING WATER DEMAND

SUPPLY SYSTEMS PREDOMINANTLY FOR FLUSH VALVES

LOAD IN WATER SUPPLY FIXTURE UNITS (WSFU)

WATER DEMAND LOAD IN WATER SUPPLY FIXTURE UNITS (WSFU)

WATER DEMAND

Gallon per minute

Liter per second Gallon per minute

Liter per second

1 - - 60 54.0 3.41

2 - - 70 58.0 3.66

3 - - 80 61.2 3.86

4 - - 90 64.3 4.06

5 15.0 0.95 100 67.5 4.26

6 17.4 1.10 120 73.0 4.61

7 19.8 1.25 140 77.0 4.86

8 22.2 1.40 160 81.0 5.11

9 24.6 1.55 180 85.5 5.39

10 27.0 1.70 200 90.0 5.68

12 28.6 1.80 250 101.0 6.37

14 30.2 1.91 300 108.0 6.81

16 31.8 2.01 400 127.0 8.01

18 33.4 2.11 500 143.0 9.02

20 35.0 2.21 750 177.0 11.17

25 38.0 2.40 1000 208.0 13.12

30 42.0 2.65 1250 239.0 15.08

35 44.0 2.78 1500 269.0 16.97

40 46.0 2.90 2000 325.0 20.50

45 48.0 3.03 2500 380.0 23.97

50 50.0 3.15 3000 433.0 27.32