Harvesting rainwater in cisterns is a lot like collecting sunshine in solar panels.
The technology exists to pull a home totally "off the grid" but the cost – and a long payback period – make it economically unfeasible for most of us. On the other hand, installing a cistern to capture rainwater for use in a Florida-friendly landscape can be an eco-smart and cost-effective alternative to potable water.
"Rain barrels look great but they're not going to make a significant impact in most landscapes," notes Dave Bracciano, demand management coordinator for Tampa Bay Water. "Harvesting rainwater for indoor use is complicated because it has to be stored, filtered and treated, but it's simpler and more cost-effective for outdoor use."
For Carl Roth, a retired engineer who recently moved to Port Richey, the primary goal was to reduce his "water footprint" with cost-effective technology. "A solar water heater with two people in the house has something like a 20-year return on investment. Installing a cistern and irrigation system was much more reasonable."Roth met with experts from the Florida Yards & Neighborhoods Program at Pasco County Extension, attended an FYN-sponsored seminar on cisterns, then did a great deal of research online before he began building the system, including a thorough review of reports from Florida, Arizona, Oregon, Texas and Virginia. "If you look before you leap, things work better," he quips.
His goal was to irrigate 900-plus new landscape plants using low-flow and mist irrigation with water collected from 3100 square feet of tile roof. Space limitations – combined with a wife who made aesthetics a top priority – limited Roth from installing a cistern large enough to capture all the rain that lands on his roof. "An inch of rain pretty much fills a 1500-gallon tank," he notes. "I was really glad that the tank overflow was sized correctly to deal with heavy rains."
Installation of the system was simple enough that Roth created a Power Point presentation (http://www.baysoundings.com/stories-images/rainwater.pps) to encourage other people to build their own. "I wanted to show 'handy' folks that the project is relatively straight-forward and should not be too daunting."
In fact, the toughest parts of the project were sourcing the cistern and then digging a hole deep enough that the 1550-gallon tank didn't dominate the yard, he said. "Do a lot of research before you buy a tank, some of them are two or three times the cost of others."
With Roth doing the installation himself, the total cost of the system was just $2250, including fittings and pipes for the irrigation system as well as an automatic controller with rain sensor. "It works even better than I expected," he said. "I had to use supplemental water when we first installed the plants, but the cistern gives me about three weeks of water using the low-flow emitters twice a week."
From a technical perspective, rainwater harvesting is so simple that people in places like Key West have been doing it for many years, adds Brian Gregson, general manager of Rainwater Services in St. Petersburg. "You catch the water on your roof, it runs down gutters and into tanks and then it's pumped back out when you need it."
Costs for professional installation can vary significantly depending upon whether a customer is looking for low-volume irrigation or a totally off-the-water-grid home that recycles "gray" water from showers and washing machines as well as capturing rain, he says. "Most of our installations are upscale new homes," Gregson said. "They're taking a whole-house approach with other green features like solar power and natural lighting. They're definitely looking at costs and return on investment but they also have strong conservation mindsets."
That was exactly the case for the owners of the region's first certified Platinum LEED (Leadership in Energy and Environmental Design) home built on Coffee Pot Bayou. "They didn't care what size or style the house was, they wanted it to be certified as Platinum LEED," notes Jimmy Brattain, president of Design Works Florida, which designed and built the home.
Three 900-gallon tanks capture about 80% of the rain that falls on the waterfront home with two of the tanks providing low-flow irrigation for a landscape that contains 100% native plants. The third tank is used for flushing toilets and includes a UV purification system as well as a connection to the city water system. "It's on a float valve so there's always water available even if we don't get any rain."
In retrospect, the design would have been significantly more cost effective if it had not called for indoor water use, Brattian notes. "It's not really a practical application for most people because city codes required that the rainwater was treated and it got a little complicated."
Because it was new construction, building the rainwater harvesting system was "nearly a wash" in terms of construction costs, he adds. "We used copper gutters but we went with less-expensive PVC pipes inside the walls to collect the water. At that point, it doesn't make sense not to harvest rainwater."
In fact, Brattian predicts that Florida building codes will eventually require that all new homes are built with rainwater harvesting systems for irrigation. "It just requires a couple of simple steps and we need to save all the water we can."
Along with the dollar savings homeowners realize, capturing rainwater helps minimize contaminants that flow into Tampa Bay. Stormwater, which picks up pollutants as it flows through yards and across parking lots, contributes more than half of the nitrogen in the bay.
Rainwater harvesting hasn't been evaluated for its impact on stormwater treatment and nutrient run-off but clearly there is an impact, Bracciano said. Most rainwater harvesting systems release the first half-inch of rain – which typically contains the highest level of contaminants – so measuring the impact isn't quite as easy as subtracting the gallons of water harvested. "We haven't done that research yet."
Roof size: Calculate square footage including space like garages and covered porches but subtract areas that would be difficult to connect by gutter.
Determine maximum capacity of your roof: Roofs act like gigantic funnels catching water. A general rule of thumb calls for a half-gallon of water per square foot per inch of rainfall. A 2000-square-foot roof could capture 1000 gallons with an inch of rain although most systems divert the first few gallons instead of allowing it in the system.
Estimate the amount of water needed: Demand varies dramatically based on the type of landscape and irrigation system. An automatic irrigation system treating 500 square feet of turf uses about 4700 gallons during the spring dry season. A manual system would only use about 2800 gallons and irrigating plants other than turf would require even less water. Optimally, the rainwater harvesting system, irrigation system and landscape will be designed to work together. If necessary, your cistern can be connected to a water supply line with a float valve so that water is available even in times of drought.
Conveyance: Do existing gutters capture all rainfall? Will additional downspouts be necessary to connect to the cistern? If your home is surrounded by trees, you may need to install leaf guards on your gutters.
Pretreatment: Will you need a first-flush device or a filter to separate out leaves and other litter?
Determine your cistern requirements:
Distribution: pump or pressure tank?