Brigit Afshar University of Texas at Austin Statistics in Water Resources May 2009.

Thirsting for Rain:Rainwater Harvesting Feasibility

Brigit Afshar

University of Texas at AustinStatistics in Water Resources

May 2009

Conventional Rainwater Harvesting System

Roof Catchment

Storage TankGutter

First-Flush Diverter10 gal./1000 sq. ft.

(TWDB)

DownspoutOverflow Spout

Adapted from: Texas Commission on Environmental Quality (TCEQ). 2007. “Harvesting, Storing, and Treating Rainwater for Domestic Indoor Use.”

Feasibility

National Atmospheric Deposition Program (NADP)

VS.

Domestic Indoor Water DemandNumber of people per household 3

Water Consumption

of Fixture Assumptions

Household Monthly (30-day) Demand

Toilets

Ultra Low Flow Toilets (post-1993) 1.6 gal/flush 6 flushes/person/day 864

Dual Flush 1 gal/flush liquids flushes/person/day 0

1.6 gal/flush solids flushes/person/day 0Baths and Showers Showerhead 2.2 gal/min 5 minutes/person/day 990Baths 50 gal/bath baths/day 0

Faucets 2.2 gal/faucet/min 5 minutes/person/day 990Appliances (per-use, not per-person) Clothes washer (Front-loading, 18-25 gal) 20 gal/load 2.6 loads/week 208Dishwasher 8 gal/cycle 0.7 cycles/day 168TOTAL 3220

Source: TWDB; AWWA,1999

AssumptionsMonthly Annual

Indoor water demand (gallons) 3220

Irrigation (gallons, Mar-Oct) 150

Collection surface (sq. ft.) 2500

Starting volume (gallons) 3000

Collection rate (gal/in. rain/sq.ft) 0.62

Collection efficiency 0.85

Indoor water demand (gallons) 38640Irrigation (gallons, Mar-Oct) 1200Collection surface (sq. ft.) 2500Starting volume (gallons) 10000Collection rate (gal/in. rain/sq.ft) 0.62Collection efficiency 0.85

Climate Regions of Texas

Source: NADP, 2009Source: Texas Center for Policy Studies, 1995

Far W

est

Hig

h Pla

ins

Lower

Gul

f

Nor

th T

exas

Nor

thea

st

Sout

h Cen

tral

Upp

er G

ulf

Wes

t Cen

tral

0

10

20

30

40

50

60

70

80

Annual Average Annual Minimum Annual MaximumA

nn

ual

Pre

cip

itati

on

(in

ch

es)

Upper Rio Grande and Far West

MonthIrrigation Demand

Total Demand (gallons)

Average rainfall (inches)

Rainfall collected (gallons)

End-of-month storage (gal)

January 0 3220 0.584 769.23 549.2317February 0 3220 0.624 822.24 -1848.53March 150 3370 0.539 709.68 -4508.84April 150 3370 0.551 726.38 -7152.45May 150 3370 1.161 1529.5 -8992.91June 150 3370 1.864 2455.6 -9907.22July 150 3370 2.486 3274.8 -10002.4August 150 3370 2.735 3602.7 -9769.67September 150 3370 2.021 2662.5 -10477.1October 150 3370 1.557 2051.9 -11795.2November 0 3220 0.775 1020.6 -13994.5December 0 3220 0.684 901.24 -16313.3

Total: 15.580 20526Ja

nuar

y

Febr

uary

Mar

ch

April

May

June Ju

ly

Augus

t

Sept

embe

r

Oct

ober

Nov

embe

r

Dec

embe

r-20000

-15000

-10000

-5000

0

5000

Rainfall Collected End-of-Month Storage

Gall

on

s of

Wate

r

Northeast

Janu

ary

Febr

uary

Mar

ch

April

May

June Ju

ly

Augus

t

Sept

embe

r

Oct

ober

Nov

embe

r

Dec

embe

r0

5000

10000

15000

20000

25000

30000

Rainfall Collected End-of-Month Storage

Gall

on

s of

Wate

r

Janu

ary

Febr

uary

Mar

ch

April

May

June Ju

ly

Augus

t

Sept

embe

r

Oct

ober

Nov

embe

r

Dec

embe

r-2000

-1000

0

1000

2000

3000

4000

5000

6000

Rainfall Collected End-of-Month Storage

Gall

on

s of

Wate

r

West Central

Annual Analysis

Far W

est

Lower

Gul

f

Nor

thea

st

Upp

er G

ulf

Reg

ion

Hig

h Pla

ins

Nor

th T

exas

Sout

h Cen

tral

Wes

t Cen

tral

-30000.00-20000.00-10000.00

0.0010000.0020000.0030000.0040000.0050000.0060000.0070000.00

Average Minimum Maximum

An

nu

al

Diff

ere

nce B

etw

een

Rain

-fa

ll C

oll

ecte

d a

nd

Dem

an

d (

t-h

ou

san

d g

all

on

s)

Texas Harvesting Potential

Region Needs Met

Water Saved (gallons/year)

Far West Partial 20118High Plains Partial 22456Lower Gulf Yes 41008North Texas Yes 42283Northeast Yes 60482South Central Yes 30177Upper Gulf Yes 55119West Central Yes 31381

United States Hydrologic Regions

Source: NADP, 2009

1 New

Engl

and

2 M

id A

tlan

tic

3 Sou

th A

tlan

tic

...

4 Gre

at L

akes

5 Ohio

6 Ten

nesse

e

7 Upp

er M

ississ

ippi

8 Lo

wer

Mississ

ippi

9 Sou

ris-

Red

-Rai

ny

10 M

isso

uri

11 A

rkan

sas-

Whit

e...

12 T

exas

-Gulf

13 R

io G

rande

14 U

pper

Col

orad

o

15 L

ower

Col

orad

o

16 G

reat

Bas

in

17 P

acifi

c Nor

th...

18 C

alifo

rnia

Alask

a

Amer

ican

Sam

oa

Haw

aii

Puerto

Ric

o

Virgi

n Islan

ds0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

Average of  Precip (in) Min of  Precip (in)Max of  Precip (in)

An

nu

al

Pre

cip

itati

on

(in

ch

es)

1 New

Engl

and

2 M

id A

tlan

tic

3 Sou

th A

tlan

tic

...

4 Gre

at L

akes

5 Ohio

6 Ten

nesse

e

7 Upp

er M

ississ

ippi

8 Lo

wer

Mississ

ippi

9 Sou

ris-

Red

-Rai

ny

10 M

isso

uri

11 A

rkan

sas-

Whit

...

12 T

exas

-Gulf

13 R

io G

rande

14 U

pper

Col

orad

o

15 L

ower

Col

orad

o

16 G

reat

Bas

in

17 P

acifi

c Nor

th...

18 C

alifo

rnia

Alask

a

Amer

ican

Sam

oa

Haw

aii

Puerto

Ric

o

Virgi

n Islan

ds-50000.00

0.00

50000.00

100000.00

150000.00

200000.00

250000.00Average Minimum Maximum

An

nu

al

Diff

ere

nce B

etw

een

Rain

fall

Col-

lecte

d a

nd

Dem

an

d (

thou

san

d g

all

on

s)

United States Harvesting Potential

Region Needs Met

Water Saved (gallons/yr)

13 Rio Grande Partial 2783214 Upper CO Partial 2368715 Lower CO Partial 1450416 Great Basin Partial 15955Alaska Partial 22725

Questions?