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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
Danilo V. Ravina New NAMPAP Cebu Chapter
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)
Danilo V. Ravina New NAMPAP Cebu Chapter
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
Danilo V. Ravina New NAMPAP Cebu Chapter
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
Danilo V. Ravina New NAMPAP Cebu Chapter
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)
Danilo V. Ravina New NAMPAP Cebu Chapter
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
Danilo V. Ravina New NAMPAP Cebu Chapter
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
Danilo V. Ravina New NAMPAP Cebu Chapter
• 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.
Danilo V. Ravina New NAMPAP Cebu Chapter
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.
Danilo V. Ravina New NAMPAP Cebu Chapter
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
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