1. Water Demand
&
Flow Calculations
Lokhaze Ali
Visiting Faculty
NICE, SCEE, NUST

2. Thought of the Day
Water Demand & Flow Calculations 2

3. Water Use
Water use can be distinguished into three
different types
1. Withdrawals or Abstractions
2. Consumptive Water Use
3. Non-Consumptive Water Use
Water Demand & Flow Calculations 3

4. Withdrawals or Abstractions
• Where water is taken
from a surface or
groundwater source
• after use returned to
a natural water body
• e.g. water used for
cooling in industrial
processes returned to
a river
• such return flows are
important for
downstream users
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5. Consumptive Water Use
• Water consumption that starts
with a withdrawal or an
abstraction but in this case
without any return flow
• water abstracted that is no
longer available for use
• it has evaporated, transpired,
been incorporated into products
and crops
• consumed by man or livestock or
otherwise removed from
freshwater resources
• e.g. water use include steam
escaping into the atmosphere
and water contained in final
products i.e. it is water that is
no longer available directly for
subsequent uses
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6. Water Demand & Flow Calculations 6

7. Water Demand & Flow Calculations 7

8. Non-Consumptive Water Use
• Water withdrawn for
use that is not
consumed
• e.g. water withdrawn
for purposes such as
hydropower generation
• recreational activities
• boating or fishing
where the water is still
available
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9. Water demand
• Volume of water
requested by users to
satisfy their needs
• Often considered equal
to water consumption
• Conceptually the two
terms do not have the
same meaning
• In rural parts of Pakistan,
the theoretical water
demand considerably
exceeds the actual
consumptive water use
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10. The 4 S’s: Some Common Terms
• Water Shortage - absolute shortage where
levels of available water do not meet certain
defined minimum requirements.
• Water Scarcity - a more relative concept
describing the relationship between demand for
water and its availability.
• Water Stress - the symptomatic consequence
of scarcity which may manifest itself as
increasing conflict over sectoral usage, a
decline in service levels, crop failure, food
insecurity etc..
• Water Security - a situation of reliable and
secure access to water over time.

11. Water Scarcity
Water scarcity category and Volume of water available
associated problems (m3/person/year)
Beyond the “water barrier”: continual, < 500
wide-scale water supply problems,
becoming catastrophic during droughts.
Chronic water scarcity: continual water 500 to 1,000
supply problems, worse during annual dry
seasons; frequent severe droughts.
Water stressed: frequent seasonal water 1,000 to 1,666
supply and quality problems, accentuated
by occasional droughts.
Moderate problems: occasional water 1666 to 10,000
supply and quality problems, with some
adverse effects during severe droughts
Well-watered: very infrequent water > 10,000
supply and quality problems, except during
extreme drought conditions. Demand & Flow Calculations
Water 11

12. Water Use
• Agricultural use - Any use or • Residential use - The use of
activity involving agriculture, water that is billed to single and
including irrigation multi-family residences, which
• Commercial use - The use of applies to indoor and outdoor
water by a place of business, uses
such as a hotel, restaurant, or
office building. This does not
include multi-family residences
or agricultural, industrial, or
institutional users
• Industrial use - The use of
water in processes designed to
convert materials of a lower
order of value into forms having
greater usability and commercial
value, and the development of
power by means other than
hydroelectric, but does not
include agricultural use
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13. Top 10 Freshwater Consumers
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14. World Water Use by Sector
Source: OECD Environmental Outlook Baseline, 2007
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15. Typical Water Use at Home
Shower 2 gallons per minute
Teeth brushing <1 gallon, especially if water is
turned off while brushing
Hands/face washing 1 gallon
Dishwasher 4 to 10 gallons/load
Dishwashing by hand 20 gallons
Clothes washer 25 gallons/load
Toilet flush 3 gallons
Outdoor watering 5 to 10 gallons per minute
Water Demand & Flow Calculations 15

16. Residential Gallons Per Capita Per Day
Residential gallons per
capita per day =
(Residential Use ÷
Residential Population) ÷
365
• Residential Use = Single-
Family Use + Multi-Family Use
• Residential Population = the
residential population of the
service area. Includes only
single- and multi-family
populations
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17. Commercial Use
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18. Water Data USGS
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19. Water Demand US
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20. Estimating Water Withdrawals for Livestock
Wt = ((Pdc * Cdc) + (Pbc * Cbc) Plh = Number of laying hens;
Clh = Coefficient for laying hens, in gallons
+ (Ph * Ch) + (Plh * Clh) + (Pbh * per day;
Cbh) + (Pt * Ct) + (Ps * Cs) + (Pg Pbh = Number of broilers and other chickens;
* Cg) + (Pe * Ce)) / 1,000,000 Cbh = Coefficient for broilers and other
chickens, in gallons per day;
where
Pt = Number of turkeys;
Wt = total water withdrawals, in million
Ct = Coefficient for turkeys, in gallons per
gallons per day; day;
Pdc = Number of dairy cows; Ps = Number of sheep and lambs;
Cdc = Coefficient for dairy cows, in Cs = Coefficient for sheep and lambs, in
gallons per day; gallons per day;
Pbc = Number of beef and other cattle; Pg = Number of goats;
Cbc = Coefficient for beef and other Cg = Coefficient for goats, in gallons per day;
cattle, in gallons per day; Pe = Number of horses, ponies, mules, burros,
and donkeys; and
Ph = Number of hogs and pigs; Ce = Coefficient for horses, ponies, mules,
Ch = Coefficient for hogs and pigs, in burros, and donkeys, in gallons per day.
gallons per day;
Water Demand & Flow Calculations 20

21. Water-use coefficients for Livestock
Water Demand & Flow Calculations 21

22. Different crops contribution to total
water footprint of crop production
Period: 1996–2005
Water Demand & Flow Calculations 22

23. The Green, Blue, Grey and Total
Water Footprint of Crop Production
Period 1996-2005
Water Demand & Flow Calculations 23

24. Urban Water Demand
in
California to 2100
Case Study
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25. Urban Water Use
Water Demand & Flow Calculations 25

26. Commercial & Industrial Water Use
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27. Simple Linear Forecasts
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28. Global Surface Warming &
Population Projections
Water Demand & Flow Calculations 28

29. Time Series of Decadal Average
Water Use for Six Simulations
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30. Simulated Urban Water Use under
Scenarios of Conservation and Population
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31. Flow Calculations
Water Demand & Flow Calculations 31

32. Conversion Factors
Multiply By To obtain
gallon (gal) 3.785 liter (L)
gallon (gal) 0.003785 cubic meter (m3)
million gallons 3,785 cubic meter (m3)
(Mgal)
gallon per day 0.003785 cubic meter per
(gal/d) day (m3/d)
million gallons 0.04381 cubic meter per
per day (Mgal/d) second (m3/s)
Water Demand & Flow Calculations 32

33. Flow Calculations
Flow is expressed in the English Flow Conversions
system of measurements using Flow rates can be converted to
many terms. The most common different units using the
terms are: conversion process.
gpm - gallons per minute The most common flow
conversions are:
cfs - cubic feet per 1 cfs = 449 gpm
second
and
gpd - Gallons per day
1 gpm = 1,440 gpd
MGD - Million gallons
per day
Water Demand & Flow Calculations 33

34. Flow Calculations
gpd to MGD MGD to gpm
To convert gallons per day (gpd) to There are many instances where
MGD, divide the gpd by 1,000,000 the design or plant information is
gallons or 106. given in MGD and we wish to have
the flow in gpm. This conversion is
For example:
accomplished in two steps.
Convert 125,000 gpd to For Example:
MGD. Convert 0.125 MGD to gpm
125,000 gpd = 0.125 MGD Step 1) Convent to gpd by
multiplying by 1,000,000
Or
0.125 x 1,000,000 = 125,000 gpd
convert 2,300,000 gpd to Step 2) Convert to gpm by dividing
MGD by the number of minutes in a day
(1,440 min/day).
2,300,000 gpd = 2.3 MGD 125,000 gpd = 86.8 or 87 gpm
Water Demand & Flow Calculations 34

35. Detention Time
Detention time is the Sample Calculation
amount of time that a fluid The reservoir for the town is
stays in a container. 85,000 gallons. The well will
produce 55 gpm. What is the
Detention time is expressed in units of time. detention time in the tank in
The most common are: seconds, minutes, hours.
hours and days.
Solution:
Detention Time = Volume DT = 85,000 gallons = 1,545 min
55 gpm
Flow Rate
or
For example: 1,545 minutes = 25.8 hrs
1) if the flow is in gpm then the detention
time will be in minutes; 60 minutes/hr
or
2) if the flow is in gpd, then the detention
time will be in days.
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36. Water Tanks
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37. Examples
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38. Examples
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39. Home Assignment
1. A tank is 20' x 60' by 15' deep. What is
the volume in gallons?
2. A tank is 60' in diameter and 22' high.
How many gallons will it hold?
3. A tank is 82' in diameter and 31 feet
high. The flow is 1600 gpm. What is the
detention time in hours?
4. A tank is 120' x 50' x 14' deep. The flow
is 2.8 mgd. What is the detention time in
hours?
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40. Safe Drinking Water for ALL
Water Demand & Flow Calculations 40

41. Thank You
lokhaze@hotmail.com
Cell: 0345-5077775