When it rains in Central Texas, it pours…and then it stops raining, sometimes for months. But rainwater collection systems help gardeners capture those downpours for use during dry seasons. Plus, rainwater’s slight acidity and lack of treatment chemicals help plants thrive. Systems that harvest rainwater for gardening range from 50-gallon DIY projects to several-thousand-gallon tanks installed by professionals. The rule of thumb: the more capacity, the better.
Generally speaking, you can collect about .6 gallons per square foot of roof surface, per inch of rainfall—or, for example, 600 gallons from a 1,000-square-foot roof from a 1-inch rainfall. Beginners should base their system choice on how much room they have for a tank (and on their budget). Don’t spend too much time calculating how much water you use; experienced rainwater harvesters say you’ll use everything you collect.
“Capacity is key,” says Rosedale neighborhood resident Jay Carpenter, who started collecting rainwater in 55-gallon barrels but soon realized they filled within the first few minutes of a storm. He scaled up to a system of three 3,000-gallon cisterns that keep his Swiss chard, tomatoes, peppers and spinach—grown in a container system that also conserves water—happily quenched throughout their growing season.
“It’s more beneficial to install as large a cistern as you can because of our feast-and-famine rain patterns,” says Chris Maxwell-Gaines, owner of Innovative Water Solutions. “You want it as large as possible so that during that rainy May, you can collect every single bit and have a full tank to use over the dry June, July and August.” Maxwell-Gaines says he encourages customers to consider bigger cisterns, because tanks get cheaper by the gallon as they get larger and relatively small increases to the cistern’s footprint can mean much bigger capacity. If a customer has room for a 500-gallon tank, he or she probably has room for a 1,000-gallon tank, which is the same height and only two feet larger in diameter.
Any type of roof material works when harvesting rainwater for gardening use, but you’ll need gutters to collect the water and funnel it into your tank or barrel. The downspout that feeds the tank will need to be shortened and tied into the tank. This task can be a DIY job that uses basic hardware-store parts, or it can be completed by a gutter contractor or a full-service rainwater harvesting company. Small 50- and 75-gallon barrels that collect water through a screened opening can simply be placed under a shortened downspout, or even where two sections of roof meet.
All gutters will need to be screened to keep out bugs and rodents as well as leaf debris, which could clog a tank. Matt Haney, founder and vice president of Harvest Rain, also recommends installing a Leaf Eater: a screen at the bottom of the downspout that filters out more debris. Sealing the tank’s inlets and outlets and screening the tank’s overflow prevent mosquito problems.
When it’s time to water, many gardeners rely on gravity and a hose (sometimes a soaker hose) attached to the base of their tank. Of course, this system works as long as the hose is below the water line in the barrel. Elevating the tank up to a foot adds additional water pressure, though it’s best to consult a professional when elevating a large tank to make sure it’s done safely. A pump will also provide more water pressure, though it requires a city permit and the addition of a backflow prevention device to keep untreated water from entering the city’s water system.
A DIY system using a 50-gallon rain barrel and hardware-store parts can cost less than $150. Full-service installation costs more: Innovative Water Solutions will install a 500-gallon tank for $1,600, and Harvest Rain’s 2,500-gallon systems start at $5,000. The City of Austin offers a rainwater-harvesting rebate of 50 cents per gallon for non-pressurized systems and $1 per gallon for pressurized systems, up to half of the system’s cost. For tanks holding 500 gallons or more, the city requires applicants to submit a design plan before approving the rebate application.
Experts agree that in most cases, a rainwater collection system won’t pay for itself; the cost of treated municipal water is simply too low to balance out the cost of a tank and other equipment. “The water is cheaper than it should be, considering how easily it can be depleted and how quickly we get into drought here,” says Ayaz Husain of the eco-minded home improvement company TreeHouse. Instead, he says, Central Texans who harvest rainwater tend to be motivated by sustainability and by the health of their plants. Plus, Husain says, in the aggregate, rainwater harvesting serves another important purpose. “If everybody had rainwater barrels we’d have much less flash flooding.”
By Robyn Ross