Rainwater harvesting is a practice that captures precipitation from a roof surface and directs it into a storage vessel for later use in the garden. This collected water is a free resource that helps reduce dependency on municipal supplies, offering both environmental and financial benefits. Plants often respond favorably to rainwater because it is naturally soft, lacks the chlorine and other treatment chemicals found in tap water, and contains beneficial dissolved atmospheric gases. Utilizing a rainwater collection system, such as a rain barrel or cistern, provides a reliable source of irrigation during dry periods.
Necessary Equipment and Sizing
A functional rainwater harvesting system requires several components. The foundation is the collection vessel, typically a durable, opaque plastic barrel or a larger cistern. A downspout diverter channels water from the roof into the barrel and allows overflow when capacity is reached. The barrel must include a fine mesh screen over the inlet to prevent debris from entering. Finally, a spigot or faucet is attached near the bottom to facilitate gravity-fed water application.
Calculating the appropriate size for a collection vessel depends on the roof area contributing to the downspout and the local rainfall patterns. A simple calculation can estimate the potential yield: multiply the square footage of the roof section by the rainfall depth in inches, then multiply that result by 0.623 to determine the total gallons captured. For instance, a half-inch of rain falling on a 1,000-square-foot roof section can yield approximately 300 gallons of water. Knowing this potential helps determine if a standard 50-gallon barrel or a much larger cistern is needed to meet gardening demands.
Installing Your Rainwater Collection System
Selecting the proper location for the barrel is the first physical step, requiring a site that is level, stable, and situated close to the chosen downspout. Because the water is typically dispensed using gravity, the barrel must be elevated off the ground, often using concrete blocks, to ensure enough clearance for a watering can or a hose connection. A full 55-gallon barrel weighs over 450 pounds, making a secure and level base a necessity to prevent tipping.
Installation requires making a precise cut in the downspout, usually with a hacksaw, at a point higher than the barrel’s inlet. The diverter is inserted into this gap and connected via a flexible hose to a sealed inlet fitting near the top of the barrel. This setup routes water directly into the container during rain. When the barrel reaches capacity, the diverter automatically redirects the excess water down the original downspout.
A second connection near the top of the barrel is necessary for an overflow mechanism. This overflow must be routed several feet away from the building’s foundation to prevent soil saturation and potential structural damage. This dual-connection system—inlet and overflow outlet—maintains a closed environment while protecting the home.
Ensuring Water Purity for Plants
Water quality is a factor when utilizing roof runoff, particularly concerning the initial surge of rain, known as the “first flush.” This first flush carries the highest concentration of accumulated contaminants, such as dust, soot, and bird droppings. A dedicated first-flush diverter is a separate chamber that temporarily separates this initial, dirtiest water from the cleaner water that follows, preventing it from entering the main storage vessel.
The volume to be diverted depends on the roof area and pollution level; a common guideline suggests diverting 5 to 10 gallons for every 1,000 square feet of roof area. A higher volume is recommended in areas with overhanging trees or high levels of airborne dust.
The composition of the roofing material can also affect water quality. Most experts agree that rainwater from standard asphalt shingles is safe for watering non-edible landscape plants. For watering edible crops, metal or tile roofs are generally preferred, or the water can be reserved for underground application.
Ongoing Maintenance and Water Application
Regular maintenance ensures the system remains functional and prevents the creation of a pest habitat. Preventing mosquito breeding is paramount, achieved by covering all openings—inlet, overflow, and spigot—with a fine mesh screen (1/16-inch or smaller). Since mosquitoes can access small gaps, sealing all pipe connections and lids tightly is advised.
If mosquito larvae are detected, a biological larvicide containing Bacillus thuringiensis israelensis (Bti) can be added. This naturally occurring bacterium targets only mosquito larvae without harming plants, pets, or humans. Periodically, the barrel should be drained and scrubbed with a mild detergent solution to remove sediment buildup or mosquito eggs. In regions with freezing temperatures, the barrel must be drained and the diverter disconnected before the first hard frost to prevent ice expansion from cracking the container or plumbing.
When applying the collected water, gardeners should focus on deep watering techniques rather than light surface sprinkling. Delivering the water slowly and directly to the base of the plant encourages the development of deep, resilient root systems. Utilizing a short hose attached to the spigot or a soaker hose allows for targeted application, ensuring the maximum benefit from the stored rainwater.