[Scpg] 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,
         energy-efficiency and the environment in mind. The Austin Energy 
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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