Rainwater harvesting is the practice of collecting and storing precipitation, usually from a rooftop, for later use. This process provides a readily available, free source of water that reduces demand on municipal systems or private wells. Capturing rainfall helps homeowners and businesses achieve greater water independence and contributes to environmental sustainability. Using this collected water decreases the energy needed for treating and transporting public water, offering financial and ecological benefits.
Uses for Landscaping and Exterior Cleaning
The most common and least demanding application for harvested rainwater is for outdoor non-potable tasks, which require minimal treatment beyond basic debris screening. Rainwater is naturally soft and does not contain the chlorine, salts, or minerals found in treated municipal water, making it particularly beneficial for plant health. Using this softer water for irrigation can nourish vegetable gardens, ornamental plants, and lawns without the mineral buildup that can occur with tap water.
For these purposes, a simple rain barrel system connected to a downspout is often sufficient to collect and store water. Beyond irrigation, harvested water is suited for various exterior cleaning projects, including washing vehicles, hosing down sidewalks and driveways, and cleaning outdoor furniture and equipment. Substituting municipal water with collected rainwater for these high-volume outdoor uses saves money on utility bills and conserves treated drinking water.
Non-Drinking Uses Inside the Home
Collected rainwater can be routed indoors for uses that consume a large volume of water but do not involve consumption. The primary indoor non-potable applications are flushing toilets and washing clothes in the laundry. Toilet flushing alone accounts for a substantial portion of a household’s indoor water usage, and using rainwater for this purpose can significantly reduce the demand on potable supplies.
Using rainwater for laundry is advantageous because its natural softness requires less detergent compared to hard tap water. Implementing these indoor applications necessitates a dual plumbing system—a separate network of pipes to deliver the untreated rainwater. This separate, non-potable plumbing is often a regulatory requirement, ensuring the collected supply cannot cross-contaminate the public drinking water supply.
Treatment Requirements for Potable Use
Making harvested rainwater safe for human consumption, including drinking, cooking, and bathing, is the most complex application and requires a multi-stage treatment train. Untreated rainwater is never safe for ingestion because it can pick up contaminants like bird droppings, dust, and microbiological pathogens from the roof surface and storage tank. The first stage involves pre-filtration to screen out large debris and sediment before the water enters the main storage cistern.
Following pre-filtration, the water must pass through a sequence of finer filters, typically involving a sediment filter and an activated carbon filter. The sediment filter removes fine particles that can cause cloudiness, while the carbon filter absorbs chemicals, pesticides, and odors to improve taste and quality. After this physical filtration, the water requires a reliable disinfection method to eliminate bacteria, viruses, and other pathogens that are too small for the filters to catch.
Disinfection is commonly achieved through ultraviolet (UV) light sterilization, which scrambles the DNA of microorganisms, preventing them from reproducing. Chemical treatment, such as monitored chlorination, is another option that provides residual protection against regrowth in the pipes. To ensure the water meets safety standards, the treated supply must be regularly tested for microbial contaminants, such as E. coli and total coliform bacteria.