Design, Maintenance, and Regulatory Considerations for a Potable Rainwater Harvesting System

When designing a rainwater harvesting system for potable use, it is important to take additional steps to ensure the water is safe for consumption and compliant with applicable regulations. These steps go beyond basic design principles—such as the WISY 4-Step Process—and may include specific treatment, certification, and monitoring requirements.

Regulatory standards can vary significantly by jurisdiction, so it is essential to consult with your local authority having jurisdiction (AHJ) to identify any relevant codes, standards, or permitting requirements. Staying informed and compliant not only ensures the safety of your system but also helps avoid potential legal or operational issues.

Potable Water Use and Third-Party Certified Equipment

To support safe potable use, many components within the system—such as post-tank filters, ultraviolet disinfection units, and pumps—are third-party tested to verify performance and reliability. While not all equipment in the system may carry formal certification, the use of proven technologies and validated treatment methods ensures the system can consistently deliver high-quality water when properly designed, installed, and maintained. Examples of third-party organizations include the National Sanitation Foundation (NSF), Water Quality Association (WQA), and IAPMO R&T. Each operates independent laboratories and performs testing identical to ANSI/NSF standards. This means IAPMO certified products undergo the same testing protocols as those certified by NSF International.

Pertinent Certifications:

NSF/ANSI/CAN 61 – establishes minimum criteria for evaluating the health effects of materials, components, products, and systems in contact with drinking water.

NSF P151 – This new program establishes guidelines for products that come in direct contact with rainwater used for drinking, including gutters, coatings, and liners placed on rooftops and ground surfaces.

IAPMO R&T – This certification assures a water systems product has undergone the same rigorous testing as the applicable NSF/ANSI/CAN performance standards and is certified as such.

WQA Gold Seal – This certification provides independent verification that products such as drinking water treatment units and components have been proven effective at reducing certain contaminants.

Roof Material

The material of your roof has a significant impact on the quality of your captured rainwater. Certain roof materials are best suited for potable applications, while others are not recommended to be used for drinking water or edible gardening applications. The table below summarizes the suitability of common roof materials for potable rainwater harvesting.

 

Suitability for Potable Use	Roof Material	Considerations
Yes, recommended	Metal; PVC; clay, ceramic, cement, or fiberglass tiles	Must have non-toxic finish and/or NSF 61 Certification.
Not recommended	Asphalt shingles	Suitability varies by product. Newer installations may leach harmful chemicals into the water. A water quality test of roof runoff is recommended.
Not recommended	Wood/shake shingles, copper, green roofs	Suitable for inedible irrigation use only.

 

Prefiltration

Effective pre-tank filtration is essential in potable rainwater harvesting systems to protect downstream treatment components and maintain water quality. Filters installed before the storage tank should be self-cleaning to minimize maintenance and prevent the accumulation of decaying organic material, which can lead to blockages and contamination.

A 400-micron or finer filtration screen is recommended for this stage, offering a balance between debris removal and flow efficiency. Products like the WISY Vortex Filters and Downspout Filters are ideal choices due to their 280-micron stainless-steel mesh construction, low maintenance requirements, and self-cleaning operation.

Storage Tank

The storage tank used in a potable rainwater harvesting system must be suitable for drinking water applications and constructed from materials that do not leach harmful substances. It is important to select tanks that have been third-party tested for potable water storage to ensure safety and compliance with health standards and comply with Food and Drug Administration (FDA) requirements.

For below-ground installations, local regulations may specify minimum setback distances from sewer lines, septic systems, and fuel storage tanks. These requirements are determined by the local authority having jurisdiction (AHJ) and should be reviewed during system design and permitting.

Pump and Pressure Tank

In a potable rainwater harvesting system, the pump and pressure tank must be suitable for drinking water applications and properly sized to meet the pressure, and flow demands of the property. Equipment should be constructed from materials safe for potable use and, where applicable, carry UL listings and third-party testing to verify performance, safety, and durability.

A UL listing indicates that a product has been tested and evaluated by Underwriters Laboratories (UL), an independent safety certification organization. UL tests products to ensure they meet specific safety, performance, and reliability standards.

For pumps and electrical components used in potable rainwater harvesting systems, a UL listing confirms that the equipment meets electrical safety standards, has been independently verified for safe operation, and is suitable for use in residential or commercial environments.

While UL listings primarily focus on electrical and mechanical safety, they complement third-party testing for potable water suitability, ensuring the equipment is both safe to operate and appropriate for use in drinking water systems.

Post-Tank Filtration

After the prefiltered rainwater is pumped from the storage tank, it is important to apply additional post-tank treatment to help ensure the water reaches potable quality. A typical approach involves three sequential stages of treatment implemented in the following order:

Stage 1: Sediment and Particulate Filtration

To further improve water quality after pre-filtration, sediment filtration is recommended to remove fine particulates such as dust, soil, and other residual debris. For potable applications, filtration down to one micron is advised. This level of filtration enhances the effectiveness of subsequent ultraviolet (UV) disinfection by eliminating particulates that could shield bacteria and pathogens from UV exposure. By reducing these potential hiding spots, the UV light can more reliably deactivate microorganisms, resulting in safer, potable water.

Stage 2: Carbon Filtration

To enhance the aesthetic and chemical quality of the water, carbon filtration is recommended. This stage helps remove organic compounds, volatile compounds, and other chemical contaminants that can affect taste, odor, and clarity. By improving these characteristics, carbon filtration contributes to a more pleasant and potable water supply, especially important for household or drinking applications. Utilizing a carbon filter is particularly important when collecting from asphalt shingles as it can reduce the potentially leaching chemicals in the water.

Stage 3: Ultraviolet (UV) Disinfection Light

As the final stage of treatment, ultraviolet disinfection inactivates any remaining pathogens, making the water safe for consumption. For potable rainwater systems, RMS recommends using a UV disinfection unit certified to NSF/ANSI 55 Class Astandards, as outlined in ARCSA/ASPE/ANSI Standard 63, the national standard for rainwater harvesting system design.

While some local jurisdictions mandate the use of NSF Class A certified UV systems for potable applications, others may not. Regardless of local requirements, RMS considers Class A certification to be best practice for ensuring reliable pathogen reduction.

If a certified Class A UV unit is not used, it is still essential to select a system capable of delivering a Class A-level UV dose of at least 40 mJ/cm² at the intended flow rate. This dosage is necessary to effectively sterilize bacteria, viruses, and other microorganisms that may be present in the water.

Maintenance and Monitoring

While selecting appropriate equipment is essential for building a reliable potable rainwater harvesting system, ongoing maintenance is equally critical to ensure consistent water quality and system performance. Regular inspection and upkeep help prevent contamination, extend the lifespan of components, and maintain compliance with health standards, which are especially important for systems intended for potable use.

Recommended maintenance activities include:

ü Cleaning roofs and gutters to prevent debris buildup.

ü Inspecting tanks and piping for leaks, cracks, or signs of algae growth

ü Cleaning or replacing prefilters as needed.

ü Verifying proper operation of pumps and UV disinfection units

ü Replacing sediment and carbon filters according to manufacturer guidelines

ü Changing UV bulbs at recommended intervals to maintain effective dosage

ü Conducting routine water quality testing to monitor microbial and chemical contaminants

By pairing intentionally designed equipment selection with a consistent maintenance schedule, you can ensure your rainwater harvesting system operates smoothly and delivers high-quality water for all household needs.