"Rainwater harvesting..." The words faded and the potential builder smirked a wee bit. He may have even winced from biting his tongue. "How big of a tank are you planning?"
"Five thousand gallons."
"Five thousand gallons! Wow! You know what you're talking about!"
Indeed, we plan to include a five thousand gallon rainwater tank in our build. The builder smirked a wee bit because he knows what we know: water goes shockingly fast. We have an 800-gallon tank at our current house, and it's amazing how quickly that water goes, especially in this wacky flood-now, drought-later Central Texas climate. A typical family in Austin will use about 2,000 to 4,000 gallons a month for the yard during the summer months. More if you have a pool. Even more if you have a garden. And even more than that if you’re washing your pigs every Thursday night. The more rain we can harvest, the better. I'd love to do 10,000 gallons (my original plan), but I'm not sure where we'd put the other tank...
Fortunately we live in a town where the city gives a rebate for rainwater harvesting systems. Austin provides 50 pennies for each gallon of your unpressurized system with the total rebate not to exceed 50 percent of the cost of your system or $5,000 over your lifetime. That's a pretty healthy rebate for rainwater. Tanks tend to run about a buck a gallon, generally less the larger the tank gets. In addition, you don't have to pay state sales tax on rainwater equipment.
Note that I wrote “unpressurized” above. If your system is pressurized, that is, you have a pump hooked up to it, something you'll need to do to run your sprinkler or even a drip system, the rebate is even better: 100 pennies per gallon. However, there's a catch: You have to install and maintain a reduced pressure zone backflow preventor, something known in the bidness as an RPZ. An RPZ has to be installed at the street near your city meter by a certified plumber (I hear estimates of $600 to 1,000) and it has to be tested annually ($100 a test) by a certified RPZ tester. The cost of that annual testing pretty much kills any money savings you might hope to achieve with a pressurized system. And RPZs are kinda ugly, sticking up out of the ground all bony and whatnot (although I imagine the good folks at the American Backflow Prevention Association [and their Texas chapters] find them rather heart-racing...).
The RPZ requirement drives urban rainwater types bug-eyed batty. The RPZ is required to protect city water supplies. If there's a pressure drop in the city system and you have a hose in your rainwater tank, your rainwater (termed “water of an unknown quality” in the RPZ subculture) may get sucked into the city’s distribution system. In that case, your neighbor may be drinking your rainwater (be sure to send him a bill!). What? You don’t plan on ever putting a hose in your tank or, if you do, you plan on having a substantial air gap (a lo-tech but effective way of protecting the city’s water supply)? Tough luck: you still need that RPZ. And the annual testing.
Until this last legislative session, it was against state law to use rainwater for potable uses in your house if you were hooked up to a public water supply system. You could use rainwater for non-potable uses such as flushing toilets and washing clothes. However, drinking rainwater is a whole nuther deal that requires filtration and a little UV to kill the wriggling nasties you don’t want in your gut. Furthermore, if you wanted to be as reliant as possible on rainwater for all of your home's needs, you'd need tanks in the 20,000 to 30,000 gallon range. There’s generally not enough back yard in town for tanks that size.
Nonetheless, I feel deeply committed to using rainwater for outdoor use at our new property. Rustling the rain conserves water, the plants like it, and, quite simply, collecting rainwater makes us happy. The tank at our current house is made by Texas Metal Cisterns, and it’s a fine tank. But my new love is made by an Australian company called BlueScope. BlueScope produces portable, galvalume, install-in-place systems with a rubber-lined storage system. And the tanks are beautiful and modern with an optional roof fascia that gives the tanks some rings-of-Saturn mid-century cache. With a diameter of 11 feet and a height of 7 feet 3 inches for the 5,000 gallon tank, she's got big feet, but she can sure hold her liquor. Because Central Texas is rainwater central USA, we can get the tank locally.
Our plan is to put the tank in the back rear of the lot and feed her from the garage roof and part of the house. We love the idea of an aqueduct running 15 to 20 feet from the garage to the tank. The local BlueScope dealer says there's no need for a first flush system if the gutters are adequately protected, but it appears the city requires one. And any system greater than 500 gallons applying for the rebate needs to have plans approved and the final system inspected by the city. So there.
How much water can you collect? The Texas Water Development Board has an easy-as-pie and coo-as-poo spreadsheet to help size your rainwater system whether it’s for indoor and/or outdoor use (much rainwater literature is directed toward rainwater drinkers…). The City of Austin uses roof area multiplied by 5 or landscaped area multiplied by 4 as a rule-of-thumb that seems somewhat reasonable.
Postnote: It turns out that the tank I love (the one pictured above) is 3,000 gallons. A smaller footprint of 8 feet 10 inches. Decisions, decisions...
It’s raining links!:
Previous post on rainwater harvesting.
City of Austin FAQ on rainwater harvesting (including quite a few on the RPZ requirement).
City of Austin rainwater harvesting factsheet.
HarvestH2O.com: An online rainwater harvesting community