Rainwater harvesting is the practice of capturing and storing precipitation rather than allowing it to become runoff. This ancient technique has seen a modern resurgence as a method to mitigate rising utility costs and reduce reliance on municipal water sources. Collecting this resource promotes water conservation during dry periods and offers a reliable, independent water supply. Harvesting systems range from simple rain barrels to complex, engineered setups involving pumps and multiple storage tanks.
Non-Potable Outdoor Applications
The simplest and most common application for collected rainwater is outdoor use, which requires minimal filtering and infrastructure. Untreated rainwater is excellent for watering gardens, container plants, and lawns because it is naturally soft and free of the chlorine and salts often found in treated tap water. Rainwater often contains dissolved nitrates and is slightly acidic, which helps plants absorb nutrients from the soil. Beyond irrigation, collected water is suitable for washing vehicles and cleaning exterior surfaces like patios, driveways, and equipment. It can also be used to top off ornamental ponds or fountains that do not contain fish.
Non-Potable Indoor Applications
Using captured rainwater indoors requires permanent infrastructure, including separate plumbing lines and a pump. Toilet flushing is an effective non-potable use, significantly reducing the volume of treated drinking water consumed daily. Laundry is another suitable indoor application, where the natural softness of rainwater requires less detergent and improves washing machine efficiency. General household cleaning tasks, such as mopping floors and washing windows, can also utilize harvested water, provided the system includes basic debris filtration. These indoor uses maximize conservation benefits throughout the year, even when outdoor irrigation is not needed.
Safe Collection and Storage Methods
Collection and Initial Filtering
The process begins with a catchment surface, typically a rooftop, which directs rainfall into gutters and downspouts. Initial filtering is accomplished by installing screens or leaf excluders at the gutter or downspout. This prevents large debris, such as leaves and branches, from entering the system.
First-Flush Diversion
A first-flush diverter improves water quality by diverting the initial volume of runoff away from the storage tank. This initial water is typically the most contaminated, carrying dirt, bird droppings, and accumulated pollutants from the roof. The diverter often uses a ball-and-float mechanism to seal off the chamber once it fills. This allows cleaner subsequent rainfall to flow into the main storage tank.
Storage Requirements
Storage tanks must be opaque and sealed to prevent sunlight exposure, which encourages the growth of algae and microorganisms. Sealing the tank is also necessary for preventing insect access, particularly mosquitoes. Tanks must be placed on a level, stable foundation to manage the substantial weight of stored water.
Treatment Requirements for Potable Use
Converting collected rainwater into water safe for drinking, cooking, and bathing requires a multi-stage treatment process addressing microbial and chemical contamination risks. Rainwater can carry pathogens and may leach contaminants from roofing materials. Treatment begins with pre-filtration to remove sediment and large particles, often using a sequence of progressively finer cartridge filters. Next, an activated carbon filter removes chemical contaminants, odors, and tastes. The final step is sterilization to eliminate microorganisms, commonly achieved through ultraviolet (UV) light disinfection or chemical treatment like chlorination. Regular water testing is mandatory to ensure the system consistently meets safety standards for human consumption.