Rainwater Harvesting

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Gutter
Downspout
Rainwater Harvesting Mike Kizer OSU Extension Ag.
Engineer
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Rainwater Collection Issues

• How much rainfall can I expect?
• Annual total
• Seasonal distribution
• How much rainwater can I collect?
• Collection area
• Storage
• How much water do I need?
• Household use
• Irrigation
• Livestock

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Oklahoma Annual Precipitation (30-year Average
1971-2000)
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Oklahoma Precipitation What is Normal?
OCS 1990 Annual Summary
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Oklahoma Rainfall What is Normal?
1998 Annual Percentage of Normal Precipitation
OCS 1998 Annual Summary
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OK Monthly Rainfall Distribution
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Rainwater Volume
Volume of water collected L x W x D 12 x 12 x 1
144 in3 1 gallon 231 in3 1 in rain 144/231
0.62 gallons / square foot of roof Not all will
make it into the rain barrel ( ?70)
D rainfall depth (1 in)
W catchment width (12 in)
L catchment length (12 in)
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Roof Catchment Area
USE THE VERTICAL PROJECTION OF THE EAVE LINE, NOT
THE SLOPED ROOF AREA
SQUARE FOOTAGE BASED ON THESE MEASUREMENTS
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Roof Catchments- Potable Water

• Preferred Materials
• Steel (galvanized, painted)
• Tile (clay, cement)
• Wood (untreated)
• Fiberglass
• Composition
• Undesirable Materials
• Tar
• Asbestos

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Rainwater Conveyance Structures(from Sustainable
Building Sourcebook)

• Slope gutters 0.5 (1 in/16 ft)
• Place gutter hangers 3 ft on center
• Use expansion joints in gutters 60 ft or longer
• 1 downspout per 50 ft of gutter length
• 1 in2 of downspout area per 100 ft2 of roof area
• Slope horizontal conveyance pipes 2 (1 in/4 ft)
• Horizontal conveyance pipes should have cleanouts
  every 100 ft
• Limit horizontal conveyance pipe bends to 45º

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Proper Rain Gutter Slope
16 Long Level Line
1 Fall
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Spacing of Gutter Hangars
3 ft
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Roof Area Downspout Size
32 ft 12 ft
1 square inch of downspout cross-section for
every 100 square feet of roof area
32 ft x 12 ft 384 ft2/100 4 in2 2 in x 3 in
minimum size
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Gutter Guard to Remove Roof Debris
Slide This Side Under Shingles
Clip This Side to Gutter
¼ to ½-inch wire mesh
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Roof Washing Before Filling Storage Tanks
Overflow hose 2-4 ft above downspout end with
small weep hole allows initial runoff and
sediment to collect in bottom of downspout.
After initial washing period, cleaner water
overflows into collection tank.
Manually operated diverter allows initial
rainfall to be wasted while roof is being washed
free of sediment.
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Roof Washer
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Roof Washer
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Roof Washer
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Roof Washer
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Roof Washer
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Rainwater Storage(from Sustainable Building
Sourcebook)

• Cisterns may be above or below ground
• Preferred materials concrete, steel, fiberglass
• Smooth interior surfaces preferred
• Use water-tight, non-toxic joint sealant
• Cover to prevent mosquito and algae growth
• Manholes should be ?24 inches wide
• Buried cistern manholes should 8 inches or more
  above original ground surface

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Large Capacity Above-Ground Cisterns
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Small Capacity Above-Ground Tanks
New 50-60 gallon Rain Barrels
(2009 Prices) Plastic 100-150 Oak
350-300
Recycled barrels Food-grade polyethylene Oak
New polypropylene rain storage barrels
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Household Water Requirements

• Typical Usage 50-100 gallons/person-day
• Toilets 0.6-1.6 gallons/flush
• Washing Machine 30-50 gallons/load
• Dishwasher 7-15 gallons/load
• Bathtub 30-50 gallons/use
• Shower 2.5-3.0 gallons/minute
• Kitchen/Bath Sinks 1.0-1.5 gallons/minute

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Summer Irrigation Water Requirements(Adequate
for flowers vegetable garden)

• Eastern OK 0.20-0.25 inch/day (20
  gallons/100 sq. ft.-day)
• Western OK 0.25-0.30 inch/day (25
  gallons/100 sq. ft.-day)
• The storage volume required makes rainwater
  irrigation makes impractical for large,
  water-intense landscapes

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Livestock Water Requirements

• Beef Cattle 8-12 gallons/head-day
• Beef Calves 1-1.5 gallons/100 lb-day
• Horses 12 gallons/head-day
• Sheep Goats 2 gallons/head-day
• Chickens 9 gallons/100 head-day

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Appropriate Pipe Sizing
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Units Conversions

• 1 acre-inch 27,154 gallons
• 1 cubic foot 7.48 gallons
• 1 cubic foot of water 62.4 pounds
• 1 gallon of water 8.34 pounds

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Rainwater Harvesting Information

• Green Building Program Sustainable Building
  Sourcebook
• www.greenbuilder.com/sourcebook/Rainwater.html
• Texas AM Rainwater Harvesting Site
• http//rainwaterharvesting.tamu.edu/

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Oklahoma Annual Precipitation (30-year Average
1961-1990)
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Pressure Requirements

• 0.43 psi for every 1 foot of vertical lift
• 10-15 psi for point-source drip emitters
• 6-12 psi for drip tape
• 30-50 psi for impact and rotor sprinklers
• 20-40 psi for spray head sprinklers
• 0.5-1.0 psi/100 feet of PVC/PE supply line

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Water Pumps
Dayton 1/3 hp, 115 v. Centrifugal Pump
Price 238 (Grainger.com) 18 psi Max. Pressure
10 gpm_at_ 15 psi
Little Giant 5/8 hp, 115 v. Submersible Pump
Price 195 (Plumbingstore.com) 13 psi Max.
Pressure 22gpm _at_ 10 psi
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Rainwater Collection(Irrigation)

• Waste initial runoff to wash off sediment
• Screen organic matter (leaves) to prevent
  fermentation

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Rainwater Collection(Drinking Water)

• Waste initial runoff to wash off sediment
• Screen organic matter (leaves) to prevent
  fermentation and disinfection by-products
• Filtration by coarse sand recommended
• Disinfection by chlorination, ozonation, or
  ultraviolet light is necessary

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Net Irrigation Water Requirement
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Homemade Roof Washer
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Water Metering
Household water meters 5/8-inch meter Approx.
110 ¼- gpm 20 gpm capacity
Auto shut-off meter 100-1600 gallons Approx. 25
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Large Capacity Below-Ground Tank (2009 Prices)
600 gal 598 1700 gal 1313 2500 gal
2361
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Circular Tank Capacity(Tank Dimensions feet
Capacity gallons)
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Square Tank Capacity(Tank Dimensions feet
Capacity gallons)
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http//www.twdb.state.tx.us/publications/reports/R
ainwaterHarvestingManual_3rdedition.pdf
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Annual Rainfall