Permits for rainwater cisterns are issued at the local level in nearly every U.S. jurisdiction, and the system you install has to comply with whichever model plumbing code your area has adopted — the Uniform Plumbing Code or the International Plumbing Code — along with any state rules on how much water you can collect and what you can do with it. No federal law regulates rainwater harvesting for non-potable use.1U.S. Environmental Protection Agency. Rainwater Harvesting: Conservation, Credit, Codes, and Cost All regulation sits with states and localities, and there is no centralized database of these rules maintained by any federal agency.2U.S. Department of Energy. Rainwater Harvesting State Regulations and Technical Resources Every state currently permits some form of residential rainwater collection, but the conditions vary enormously, so the right first move is a phone call to your local building department before you order any equipment.
Who Issues the Permit
Most cistern projects fall under the jurisdiction of the local building department, the environmental health office, or both. Which agency takes the lead depends on how the water will be used. Outdoor irrigation often routes through the building department alone. Indoor non-potable use — toilets, laundry — generally pulls in the health office as well, because connecting rainwater lines to the building’s plumbing raises the cross-contamination stakes.
Permit fees vary widely by jurisdiction. Some jurisdictions also require a separate plumbing permit for the indoor connection on top of the general building permit for the tank and site work.
What Goes Into the Application
A complete application typically includes three documents:
- A site plan showing the cistern’s location relative to property lines, structures, septic systems, and wells.
- Manufacturer specifications — cut sheets and material certifications for the tank, pump, filters, and backflow prevention devices.
- An intended use statement specifying whether the water will feed subsurface irrigation, above-ground irrigation, or indoor non-potable fixtures like toilets.
Submit the complete package before ordering equipment. Reviewers sometimes require changes to tank placement, overflow routing, or pipe materials that affect what you buy. Starting construction without an approved permit risks a stop-work order and the possibility of having to remove work already completed.
The Plumbing Code Your System Has to Meet
The single biggest regulatory concern with any rainwater system is cross-contamination. If untreated rainwater backflows into a municipal drinking water line, it puts everyone downstream at risk. Both major model plumbing codes address this directly, and whichever one your jurisdiction has adopted is what your reviewer will check against. Roughly half the country follows each.
Chapter 16 of the Uniform Plumbing Code governs non-potable rainwater catchment systems and covers system design, permits, component identification, maintenance schedules, water quality minimums, and storage tank requirements.3IAPMO. 2018 Uniform Plumbing Code Chapter 13 of the International Plumbing Code similarly governs the materials, design, construction, and installation of non-potable rainwater collection and distribution systems.4ICC. IPC 2021 Chapter 13 Nonpotable Water Systems
Backflow Prevention
Both codes require backflow prevention wherever a rainwater system connects to a potable water supply. The UPC specifically calls for either a reduced-pressure principle backflow prevention assembly or an air gap at the connection point.5IAPMO. 2021 Uniform Plumbing Code These devices ensure water can only flow in one direction. Skipping this requirement is the fastest way to fail an inspection and, in many jurisdictions, the violation that triggers the steepest penalties.
Pipe Labeling
Non-potable distribution pipes need clear identification. Under the model codes, rainwater pipes must be purple or carry purple identification tape marked “CAUTION: NON-POTABLE WATER — DO NOT DRINK,” with markings repeated at least every 25 feet and at every wall, floor, or ceiling penetration. The color coding exists so that any plumber or inspector working on the building years later can immediately distinguish rainwater lines from drinking water lines.
Tank Openings
Every tank requires a sealed lid and screened openings. The EPA specifies #24-mesh non-corrodible screens on vents and overflow pipes to block mosquitoes and other insects, with stainless steel as the preferred material.6Environmental Protection Agency. Sanitary Protection of Drinking Water Storage Tanks: #24 Mesh Non-corrodible Screen The EPA recommends consulting a professional engineer to ensure adequate airflow is maintained when installing screens on any openings.
State Rules That Sit on Top of the Local Permit
Local permit approval is not the only hurdle. State law may cap how much water you can store, restrict where you collect it from, limit what you use it for, or require a licensed engineer on the design.
A handful of states impose hard volume caps. One state limits residential collection to two barrels with a combined capacity of 110 gallons, restricted to outdoor use on the same property. Another caps unregistered collection at two containers of no more than 100 gallons each, while registered users can store up to 2,500 gallons. At least half a dozen states require that collection happen only from rooftop surfaces, and several restrict use to non-potable outdoor purposes like irrigation and gardening.
Some states require permits or professional engineering involvement regardless of local rules. A few mandate that systems be designed by a licensed professional engineer. Others only trigger permit requirements when the water is used for anything beyond basic domestic purposes or when irrigation exceeds a certain acreage. States that allow indoor non-potable use generally impose stricter treatment and plumbing requirements than those limiting use to outdoor irrigation.
Health departments in many jurisdictions set additional water quality standards for harvested rainwater used beyond basic landscape watering. Homeowners’ association restrictions vary as well, though a growing number of states have passed laws preventing HOAs from banning rainwater systems outright. Before purchasing equipment, check your state environmental agency’s website and call your local building department. The five-minute phone call that confirms your planned system size and use are allowed is the cheapest step in the entire project.
Sizing and Siting Questions the Reviewer Will Ask
A permit reviewer wants to see that the tank is sized to a realistic use pattern and placed on ground that can hold it.
The EPA’s formula for estimating collection potential multiplies the building footprint available for collection (in square feet) by the monthly or annual rainfall (in inches) and a conversion coefficient of 0.623 to produce gallons.7U.S. Environmental Protection Agency. NEWR Non-potable Environmental and Economic Water Reuse Calculator Resources A 1,500-square-foot roof in an area receiving 30 inches of rain annually could theoretically capture around 28,000 gallons, though actual yields run lower once you account for evaporation, gutter losses, and the first flush volume diverted away from storage. Match the tank to usage, not maximum theoretical yield. A modest garden may need only 500 gallons of storage; supplying toilets and a washing machine year-round pushes you into several thousand.
Siting matters as much as sizing. Water weighs 8.34 pounds per gallon. A 1,000-gallon tank holds over 8,300 pounds of water alone, plus the weight of the tank itself. That load concentrated on a small footprint can crack a patio, sink into soft ground, or exceed the capacity of a deck. Above-ground tanks need a level pad of compacted gravel, compacted sand, or a poured concrete slab. Underground tanks require excavation and a gravel bedding thick enough to distribute the load and allow drainage around the tank. For systems exceeding about 1,000 gallons, having a structural engineer or the tank manufacturer confirm the foundation is worth the modest cost.
Final Inspection
After installation, a final inspection with a certified plumbing inspector verifies that the system matches the approved plans. Inspectors typically check for proper venting, overflow drainage routing, backflow prevention device installation, and correct non-potable pipe labeling. The system is not legally operational until the inspector signs off.
Keep a maintenance log once the system is running. Many jurisdictions require one under their adopted plumbing code, and it protects you if questions arise during a property sale or code compliance review.
Potable Use Is a Different Permit
Everything above assumes non-potable use — irrigation, toilet flushing, laundry. Converting harvested rainwater to drinking water is a separate undertaking that involves multi-stage treatment and, in most jurisdictions that allow it, ongoing testing and monitoring.
The general treatment train for potable rainwater starts with pre-filtration (typically 5 to 30 microns) to remove particulates, followed by a finer micro- or ultra-filtration stage in the 0.01 to 0.1 micron range that targets bacteria and parasites. UV disinfection follows, with Class A systems delivering a minimum UV dose of 40 millijoules per square centimeter under NSF/ANSI Standard 55. A Class A UV system must include a light sensor that monitors UV intensity and a safety shutoff that stops water flow if UV output drops below effective levels. Storage tanks and components in contact with potable water should meet NSF/ANSI Standard 61, which tests for chemical contaminants that may leach from tank materials into drinking water.8NSF. Poly Processing Chemical Storage Tank Certification Certification covers not just the tank walls but fittings, gaskets, and other accessories in contact with the water.
The ARCSA/ASPE Rainwater Catchment Design and Installation Standard provides professional guidance for potable applications, though it is not a federal regulation.1U.S. Environmental Protection Agency. Rainwater Harvesting: Conservation, Credit, Codes, and Cost If you are seriously considering potable use, hire a licensed engineer experienced with rainwater treatment. The equipment costs more, the permitting is more involved, and the consequences of getting it wrong are serious.