Collecting rainwater is one of the smartest things a gardener can do. No chemicals and it's free!
We have the simplest collection system imaginable. The downspouts from our house and workshop run into 66 gal. barrels. We put mosquito donuts (cut into 1/4s with 1/4 per barrel) in the barrels, and replenish the donuts when needed.
Ours is a "lift and carry" system. I dunk a bucket or watering can into the barrel and carry the water to where it is needed. People have asked if we could add spigots, connect hoses, do a drip system off the barrels. Probably, but this works, is simple, has no maintenance to speak of, and we're happy with it. A half-inch of rain gives us about 200 gallons of water, and we'll have more as soon as we get the guttering up on the barn.
We use plastic guttering and downspouts because it's cheaper than aluminum, and easier to hang.
I don't know where you are, but in Waco the Habitat for Humanity runs a Restore which carries excess materials donated by DYI'ers and contractors. If there is something comparable in your area, you might let them know you want guttering and downspouts. The barrels can be found on Craig's list or from a business that buys non-toxic things in large barrels (check out your local water department). I suggest fiberglass if you can get them. They are lighter weight to handle, and don't fail as quickly as the metal ones.
Happy water harvesting!

marlingardener - thank you so much for your information. About have many barrels do you need per sq ft of roof in TX? I see it often quoted for places that don't get 2" of rain in 30 min. Do you have an overflow or does your barrels just overflow onto the ground when full?

Also did it evaporate a lot during dry spells?

here is mine:

www.plantsloverain.com

I have no idea how many barrels per square foot of roof area! We just collect water, and if there is too much, it overflows (be sure you have a relief hole in your barrel). During dry spells we are using the water at a rate that negates the possiblity of evaporation. We are going to try to connect two barrels to collect the water off the barn roof. If we can figure out a way to do this with minimum difficulty, we'll post our results.
Glad you found some benefit from our experiences!

Please check with your local Texas AgriLife Extension Agent (formerly called County Extension Agent) for classes! This has become a hot topic and there are really inexpensive classes offered to the public on Rainwater Harvesting. BTW, 550 gallons can be captured from a 1000 sq ft roof wwith 1 inch of rain.

Austin has a great incentive program:
Rainwater Harvesting Incentive program

Pam

Here is a link that might be useful: TAMU link

I am in the process of installing a rainwater collection system, so you may get more information here from me than you wanted. :-)

I already have four 75 gallon barrels purchased at $60/barrel from the City of Austin and am buying two 500 gallon black polypropylene (sp?) tanks from my neighbor. (My neighbor's wife was a Master Gardener who passed away recently so he's selling them to me.)

Initially, I contacted a company in Austin for an estimate to install a 1,500 gallon tank, but their cost was extremely expensive for me--$3,600 dollars without a pump--and I think that did not include the purchase of the tank.

I also looked at this site when I considered buying a tank: http://www.plastic-mart.com/class.php?cat=9

I like the look of a metal tank best, but apparently they don't hold up as well as other kinds of tanks or so I hear.

I have a friend/contractor who has been looking at this site to help him install the tanks from my neighbor:

http://www.twdb.state.tx.us/publications/reports/RainwaterHarvestingManual_3rdedition.pdf

He is concerned primarly about building a platform that will handle the weight of the tanks when full. My property has a slight slope and I want them to gravity-feed so they must be raised a bit. I don't want to have to use a pump.--For me, it's just one more thing that could break. I'm in to low-tech!

By the way, the City of Austin will not provide a rebate for tanks that are metal or are on wooden platforms. Since I plan to put my tank on a pressure treated wooden platform, I won't be eligible for their rebate. :-(

Recently, I was lucky enough to sit by a man at a conference who installed both of the rainwater tanks at the Zilker Botanical Gardens. He gave me great information & his phone number for further questions. He said these tanks can be put on a bed of sand/granite sand or small rocks as long as there is a perimeter of pressure treated wood or concrete to hold the sand/rocks in place and as long as the subsoil is stable.

Of course one could also place tanks on a concrete slab. Since I will need a platform that's atleast 2 feet high, neither sand or concrete would work well for me.

Don't know if this was helpful. Feel like I was rambling. Good luck!

We have 2-330 gal. cube, 8-50 gal., 3-27 gal. and 1-1550 gal. tanks. The cube tanks were purchased at the local feed store for $100 each and previously contained hot sauce. The 50 gal. were purchased from the local organic landscape company for $5 each, they were used for liquid organic ingredients like molasses, fish emulsion, etc. We got the 27 gal. from a little old guy at First Mondays in Canton for $7 each. And the 1550 gal. from Tractor Supply for about $700.

Awesome information everybody!! I really appreciate it. Great links too. Seems like we should be able to collect a fairly good amount of water.

So does the plastic tanks last? I'm wondering about UV breaking them down.

You either buy UV resistant plastic or you paint them to withstand the sunlight and heat.

Pam

I have a little fistful of links covering a good range of things to consider when thinking about harvesting rainwater. I'll post them tomorrow morning.

In the meantime, these guys have a good chunk of the goods you'd need to set up your system, but check out the yellow links on the left for some installation info: http://www.tank-depot.com/tanks/rainwater.aspx

Here is a link that might be useful: Rainwater Collection Systems and Info

I know this is complete overkill, but I promised:

Wiki Rainwater Tank Overview: http://en.wikipedia.org/wiki/Rainwater_tank
Australian Guide for Rainwater Systems: http://www.yourhome.gov.au/technical/fs73.html
WaterSmart How To Configure Domestic Rainwater Tanks : www.gosford.nsw.gov.au/environment/education/documents/fact-sheets-2/4_rainwater_tanks.pdf
Environmental Health Directorate Rainwater Pamphlet: http://www.health.wa.gov.au/envirohealth/water/docs/Country_Rainwater_Collection.pdf
Environmental Health Directorate Urban Rainwater Collection Pamphlet: http://www.health.wa.gov.au/envirohealth/water/docs/Urban_Rainwater_Collection.pdf
80 Page Guidance on Use of Rainwater Tanks: http://enhealth.nphp.gov.au/council/pubs/pdf/rainwater_tanks.pdf
NSW Health Department's Tank Maintenance Guidelines: http://www.rainharvesting.com.au/FileLibrary/nsw_health_dept_tank_guidelines_apr2004.pdf
Rainwater Glossary : http://www.rainwaterglossary.com/content/view/12/26/
10 Steps to Rain Harvesting Sustainable Water : http://www.rainharvesting.com.au/FileLibrary/10_steps_to_rh_sustainable_water_11.8.05.pdf
Sydney Waters guide to buying a rainwater tank : http://www.sydneywater.com.au/Publications/FactSheets/RainwaterTanksBuying.pdf#Page=1
Sydney WaterÂs guide to installing a rainwater tank : http://www.sydneywater.com.au/Publications/FactSheets/RainwaterTanksInstallation.pdf#Page=1
Virginia Rainwater Harvesting Manual 2007 : http://www.cabellbrandcenter.org/Virginia%20Rainwater%20Harvesting%20Manual.pdf
Water Quality in Kentucky: Cisterns for Kentucky : http://www.ca.uky.edu/agc/pubs/ip/ip4/ip4.htm
Home Use of Graywater, Rainwater Conserves Water--and May Save Money : http://ag.arizona.edu/AZWATER/arroyo/071rain.html
Rain Water System Design Report : http://www.watgreen.uwaterloo.ca/projects/library/760/final.html
U.S. Average Annual Precipitation Maps : http://www.wrcc.dri.edu/precip.html
What is your water footprint? : http://h2oconserve.org/home.php?pd=index
Harvesting Rainwater with Rain Barrels, an Old Idea with a New Following (need to remove some links) : http://rainbarrelguide.com/
GreenBuilder Harvested Rainwater Guidelines : http://www.greenbuilder.com/sourcebook/RainwaterGuide1.html
Flow in Gutters & Downpipes : http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/rn/rwh/ugp_still_2001/ugp014_still.pdf
The Optimum Sizing of Gutters for Domestic Roofwater Harvesting : http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/wp/wp56/wp56.pdf
RHRG RECOMMENDATIONS FOR DESIGNING RAINWATER HARVESTING SYSTEM TANKS : http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/reviewed/rwh/eu/a6.pdf
Domestic Rainwater Harvesting Design & Insect Breeding: http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/reviewed/rwh/eu/c4.pdf
Reducing Mixing Effects In Water Storage Tanks : http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/rn/rwh/ugp_manson_2000/ugp002_manson.pdf
Harvesting, Storing, and Treating Rainwater for Domestic Indoor Use : http://www.tceq.state.tx.us/files/gi-366.pdf_4231966.pdf
Rainwater Harvesting and the Plumbing Codes : http://www.plumbingengineer.com/march_07/rainwater.php
Rainwater Harvesting Potential and Guidelines for Texas : http://www.twdb.state.tx.us/iwt/rainwater/docs/RainwaterCommitteeFinalReport.pdf
A Cost-Benefit Analysis of Rainwater Harvesting at Commercial Facilities in Arlington County, Virginia : http://dukespace.lib.duke.edu:8080/dspace/bitstream/10161/512/1/MP_wdh11_a_200805.pdf
A Spouse's Guide to Building the Perfect Rain Barrel System : http://www.emmitsburg.net/gardens/articles/adams/audrey/water_barrel.htm
Rainwater Harvesting - Pumps or Pressure Tanks : http://www.harvesth2o.com/pumps_or_tanks.shtml

Rainwater Tanks Revisited: new opportunities for urban water cycle management
Preface: http://www.eng.newcastle.edu.au/~cegak/Coombes/preface.pdf
Chapter 1 Introduction: http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter1.pdf
Chapter 2 The Figtree Place Experiment : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter2.pdf
Chapter 3 The Maryville House Experiment : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter3.pdf
Chapter 4 Rainwater Tank, Water Quality and Public Health Issues : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter4.pdf
Chapter 5 Institutional Resistance to the Use of Rainwater Tanks : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter5.pdf
Chapter 6 An Allotment Water Balance Model : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter6.pdf
Chapter 7 The Impact of the Use of Rainwater Tanks in Subdivisions : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter7.pdf
Chapter 8 A Regional Water Demand Model : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter8.pdf
Chapter 9 Analysis of the Water Supply Headworks Systems for the Lower Hunter and Central Coast Regions: http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter9.pdf
Chapter 10 A Community Based Investment Model to Assess the Economic Benefits of Rainwater Tanks : http://www.eng.newcastle.edu.au/~cegak/Coombes/Chapter10.pdf
Chapter 11 Summary and Conclusions : http://www.eng.newcastle.edu.au/~cegak/Coombes/Conclusions.pdf
References : http://www.eng.newcastle.edu.au/~cegak/Coombes/References.pdf

Video Resources
Rainwater Harvesting: Residential & Commercial Applications : https://admin.acrobat.com/_a781915736/p19747194/
This Old House's Roger Cook - how to install rainwater collection : http://link.brightcove.com/services/link/bcpid988221510/bclid979509284/bctid979466702

Steve Fisher's Rainwater Collection
Part 1 - Walkthrough : http://www.vimeo.com/1303028
Part 2 - The Roof : http://www.vimeo.com/1309914
Part 3 - Pre-Storage Filtration and Plumbing : http://www.vimeo.com/1310414
Part 4 - Post-Cistern Sanitation and Pumping : http://www.vimeo.com/1289985

Innovative Rainwater Harvesting - http://www.skillsone.com.au/Industry/3/Metals-Engineering/Video/557/0/Innovative-Rainwater-Harvesting/

Regarding plastic tanks, most of the large plastic tanks you see online, like the TankDepot.com tanks, are rotationally molded polyethylene. You can expect 5 to 15 years of service from them. Since your application is water, you're looking at the higher end of the spectrum at 10-15 years. I can't speak for every tank manufacturer out there, but at least Ace, Chem-Tainer, Norwesco, and Snyder use UV stabalized resins that include UV inhibitors, which will not only increase the life expectancy of the tank, but will help reduce algae growth. Getting a tank in Black would be ideal, as it would slow the algae growth the most, green and blue are good, but not as well as black, and white is the worst.
Speaking of algae growth, I went to a RWH seminar, one of the most interesting tidbits I learned: When inspecting a plastic cistern (underground water tank), it is not uncommon to find some algae inside the tank on the top!! Some UV actually penetrates the soil and the tank. That blew my mind; it's completely underground, who would'a thought.

Anyway, while the tank may last you 10-15 years, I wouldn't expect the same life out of the fittings, unless you go Stainless. My educated guess is 3-5 years, depending on exposure to sun, temperature changes, and stress.

I've done the most inexpensive rainbarrels. I used 4 33 gal trashcans with window screen over the top to keep out the mosquitoes. The netting worked better than the bt and was less than the bt even with the initial purchase of screening. It was held in place by flexible wire but a bungie cord would work even better.

My new house only has one unusable area with guttering. I intend to install my own guttering this winter. My DH's work has several 250 gallon containers with cages (for the vine to climb up when I hide them) that were used to take water to a rural area. I really hope we can get at least 3 or 4. The site that I'm putting them is level and they will also help insulate my home on the north/west side where the harshest weather is.
I will direct the water through a strainer in a smaller hole at the top.
I also plan to install roof washers to collect the debris before it goes to the tanks. Here's an explanation of a roof washer that I could find. Mine will just be a straight pipe that I open and drain. None of my equipment will go underground.

I have a whole rainwater system foe all our needs. We had Charles Gibson of Rain Man install our . They are Fiberglass ordered from Brenham TX. It is a 20,000 gal. system. We have never run out. I have a leaky 2000 gal metal tank that I am patching up for my front porch. We have never run out of water. I am off the city water system and the water tables out west of Austin are dropping with all the growth that is happening. I love the water that comes out of it.

Thank you for all the great information!!! I'm slowly going to be wading through it and see what we can do. I'm leaning towards the really simple system of just a barrel and gutter spouts into them.

What I've not figured out is how to do the watering part with gravity fed if at the same level as the barrel to still get to use most of the water. I guess I could use something to raise them.

We have most of ours on two layers of cinder blocks which raises them up about 16". DH added a hose faucet to the bottom of each of the barrels that attach to drip lines in the garden beds. The cubes are one layer and that seems to work just fine.