Rainwater harvesting provides a superior water source for plants due to its natural softness, neutral pH, and lack of chlorine and other chemical additives found in municipal water supplies. These qualities ensure healthier soil microbial life and prevent chemical buildup that can harm sensitive plants. Storing this resource effectively requires a system that prioritizes clean collection and long-term water preservation. This guide details the practical steps for setting up a reliable system, from initial capture to maintaining water quality.
Setting Up the Rainwater Collection System
The process of collecting rainwater begins with the catchment surface, typically a roof, and the existing gutter and downspout structure. A functional system requires downspouts to be connected to a conveyance pipe that directs flow toward the storage vessel. This pipe should maintain a continuous, slight downward slope to ensure water moves efficiently by gravity and avoids standing water pockets.
Before water reaches the storage container, it must pass through pre-filtration to remove large debris. Installing a screen or mesh (a leaf-eater) at the top of the downspout prevents leaves, twigs, and large insects from entering the pipework. This initial screening reduces the sediment load and potential for clogs further down the line.
A more advanced collection step involves the use of a first-flush diverter, designed to exclude the initial, dirtiest volume of rainfall. When rain first hits a dry roof, it washes off accumulated dust, bird droppings, and other contaminants. The diverter routes this initial, contaminated runoff into a separate chamber, where a floating ball rises to seal the chamber once full. This action then redirects the cleaner, subsequent rainfall into the main storage system.
The volume of water diverted is calculated based on the size of the roof, with an estimated half-gallon of water per 100 square feet of roof area recommended for this initial exclusion. After the rainfall event, the diverter slowly releases the trapped first-flush water through a small drain hole, resetting the system for the next storm. Utilizing this device significantly improves the quality of the water, reducing the need for extensive filtration later.
Selecting and Preparing Storage Vessels
Choosing the right container is essential for effective rainwater storage, ranging from rain barrels to large cisterns. Polyethylene plastic and metal tanks are common choices. For plant use, the material must be non-reactive and, ideally, food-grade if plastic, to avoid leaching chemicals. Size selection should be based on local rainfall patterns and intended usage, ensuring the vessel holds enough water to last between rain events.
The most important consideration for the vessel is its opacity, as light penetration directly encourages the growth of algae. Tanks should be made of a dark, opaque material that completely blocks sunlight from reaching the water inside. If using a translucent vessel, such as an Intermediate Bulk Container (IBC) tote, it must be painted a dark color or otherwise covered to prevent photosynthetic growth.
Proper placement of the storage vessel requires a level and stable foundation that can support the considerable weight of a full tank; water weighs approximately 8.3 pounds per gallon. Elevating the container slightly on concrete blocks or a sturdy wooden platform utilizes gravity to provide adequate water pressure for hose or watering can access. This elevation eliminates the need for a pump for simple irrigation tasks.
All access points to the vessel (lid, inlet, and overflow) must be fully sealed with fine mesh screens to prevent debris and insect entry. The overflow mechanism is a necessary safety feature that prevents water from backing up into the collection system or causing hydrostatic pressure damage. It should be directed a safe distance away from the home’s foundation to prevent water damage or erosion.
Ensuring Long-Term Water Quality
Maintaining the quality of stored rainwater primarily focuses on minimizing biological contamination and sediment accumulation. The use of opaque containers and completely sealed openings is the first and most effective defense against the growth of algae, which requires sunlight to photosynthesize. Excluding light prevents the proliferation of these organisms, keeping the water cleaner and reducing the potential for odors or blockages.
The sealed nature of the container is a defense against the introduction of mosquito larvae, which only need a small amount of stagnant water to breed. If a system is sealed with fine mesh screens over all vents and openings, larvae cannot be introduced, preventing the stored water from becoming a breeding ground. For added protection, a non-toxic biological larvicide, such as Bacillus thuringiensis israelensis (BTI), can be safely added to the water, as it specifically targets mosquito larvae without harming plants, pets, or humans.
Routine maintenance is necessary to address the small amount of sediment that inevitably enters the system despite pre-filtration. Periodically, the sediment layer at the bottom of the barrel or cistern should be flushed out through a drain or spigot located near the base. This seasonal cleaning, particularly after periods of heavy use or long dry spells, removes the fine particles that can otherwise decompose and negatively affect water quality.
The screens and first-flush diverter require occasional inspection and cleaning to ensure they are free of clogs from accumulated debris. Adhering to a simple schedule of checking the screens, flushing the sediment, and maintaining the container’s opacity and seal ensures the stored rainwater remains a high-quality resource for plant irrigation.