[Ccpg] Welcome to Austin Energy's Green Building Program. Rainwater Harvesting
Wesley Roe and Marjorie Lakin Erickson
lakinroe at silcom.com
Sun Feb 1 11:42:06 PST 2004
Welcome to Austin Energy's Green Building Program. If you're a homeowner,
renter or a member of the
design and building profession, we have information to help you
design and build with health,
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Green Building Program is nationally
known for expertise in "green" residential and commercial
construction.
http://www.ci.austin.tx.us/greenbuilder/
New on the Site
Seven Steps to Green Building (.pdf download) - Basic guidance to
make your house green
Rainwater Harvesting is the topic of our lastest factsheet see
below
Calendar of Events - Mostly local Austin sustainable building
(and related) events
Green Building Program Newsletter - January 2004 Issue
Rainwater harvesting is an old idea that is popular again
Rainwater harvesting is an old idea that is popular again. The future of
our region depends, in part, on
innovative approaches to water supply. In Central Texas, if you
have a roof area of 2,500 square feet and a
yearly average rainfall of 32 inches, you can collect almost
45,000 gallons of rainwater in a typical year.
Obviously, rainwater harvesting is potentially a viable method
to achieve sustainability with regards to
water resources. Many old homesteads and farms had rainwater
cisterns as their main source of drinking
water.
Water flows downhill
.
The basic concept of harvesting rainwater is simple. Rainwater
is mostly collected from the roofs of
buildings. It flows by gravity through gutters and downspouts
into a storage tank. From the tank it can be
used in the landscape as is, or be filtered and treated to
become a source of high-quality drinking water.
Since most of our rainfall occurs in large storm events, the
ability to store collected rainwater is
paramount. Farmers and ranchers know the value of stored water
as evidenced by today's major sources
for large water tanks- fence, ranch, and feed stores. But,
garden and nursery retailers sell smaller
rainbarrels and the City of Austin Water Conservation Program
offers 75-gallon barrels at a subsidized
cost (see 'Resources' section for more information).
All of the components for rainwater harvesting can be found in
the plumbing section of area retailers. A
typical system replaces metal downspouts with solvent-welded PVC
piping. By making the downspouts
watertight, water can be carried by gravity to a storage tank.
Several downspouts can be joined together
into one larger main pipe leading to the tank. This main pipe is
usually buried below ground and breaks
the surface again at the side of the tank. An inlet to the tank
is installed as high as possible to maximize
storage capacity. The inlet can be on the side or the top of the
tank. Just remember, the solid PVC piping
system (downspouts) at the building must be at least 6 inches
(preferable 18 inches) above the highest
piping at the tank. This will allow the tank to fill, as the
pressure of the water will work like a "P" trap under
a sink. The water will equalize and flow into the tank. This "P"
trap part of the system also must have an
outlet installed to allow water to drain out for maintenance and
to prevent freezing.
Diagram of Simple Rainwater
Collection System
for Landscape Use
There are many ways to
harvest rainwater for
landscape use. This simple
system provides for an
additional valve controlled
inlet into the bottom of the
tank. Most tanks come with a
2" bulkhead outlet. In
this illustration, when the
valve is open, water will fill
the tank from the bottom. If
there is a large volume of
water, the top inlet will
also flow. With the valve open,
water will flow out the two
hose bibs. When selecting
fittings, think of which way
the water is flowing.
Several shapes may be
available and one may be
better than the other.
Keeping the rainwater clean
Leaves, twigs, dust and bird droppings can be screened out of
your system in several ways. The simplest
method is a first-flush filter. The "first flush" of rainwater
is sacrificed to make the rest of the water cleaner.
Each downspout can direct the water to a plugged pipe that looks
much like the typical downspout,
except it has a sewer cleanout plug at the bottom. When the plug
is in, the water fills the downspout until
it reaches the top. From here, the water is directed down to the
collection pipe, which goes into the tank.
Each of these first-flush filters should be drained of debris
after each rain to be ready for the next rain
event. If your tank is full, just open the sewer clean-out plug
and the first-flush filter works like a normal
downspout.
Other devices can be used to filter the water going into a tank.
Some are large, fiberglass boxes with
30-micron filters inside to screen out the particles. Since
these filters require cleaning and maintenance,
using the first-flush filter ahead of them increases the time
between cleaning or replacement.
Using your rainwater
A gravity system uses the water from the tank via water hoses,
buckets, and soaker hoses. There is only
0.43 PSI. (pounds per square inch) per foot of water elevation.
So a full tank ten feet tall has less than 5
PSI. Even a drip-irrigation system needs at least 15 PSI. You
eventually may want to pressurize your
system using the same components you see used on water wells:
pump, pressure tank and fine mesh
filter. This creates a more usable system, but adds to the
overall cost and maintenance. City of Austin
water customers can receive a $500 rebate for a landscape
rainwater system.
Rainwater for drinking
A drinking water quality rainwater system costs about as much as
the typical well. With 20,000 to 30,000
gallons of storage, a family of four can be comfortable without
a well or piped water service. But, families
using rainwater as their sole source of potable water seldom
have lush landscapes. Just watering the
grass on a quarter-acre home site one time can use more than
3,000 gallons of water. We average about
32 inches of rain per year in this area, but much of it comes in
downpours and your tank(s) may be full
and not able to capture all of a rainfall. The time between
rains can be long, so rainwater harvesting goes
hand-in-hand with water conservation.
To make rainwater safe to drink, additional filtration is
needed, plus perhaps an ozone system, reverse
osmosis and/or ultra-violet irradiation. You become your own
water purveyor and the health of your family
and guests depends on the design and safe operation of your
drinking water system.
Resources
American Rainwater Catchment Systems Association (ARCSA)
www.arcsa-usa.org
International Rainwater Catchment Systems Association (IRCSA)
www.ircsa.org
Texas Water Development Board's Texas Guide to Rainwater Harvesting
www.twdb.state.tx.us/publications/reports/RainHarv.pdf
City of Austin Water Conservation Program's rebates,
rainbarrels, system installers or retailers
www.cityofaustin.org/watercon/rainwaterharvesting.htm
Rainwater system manufacturers, suppliers or installers
www.cityofaustin.org/watercon/downloads/rain_harvesting_contacts.pdf
Schematic of a simple, gravity rainwater harvesting system with
several options
www.cityofaustin.org/watercon/rainwaterschematic.pdf
Green Building Program Contact
Dick Peterson (512) 322-6172 or dick.peterson at austinenenergy.com
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