In an era of increasing water scarcity and environmental responsibility, commercial buildings are becoming more aware of the need to reduce their dependency on municipal water supplies. One sustainable solution that’s gaining popularity is rainwater harvesting (RWH). For buildings that were not originally designed with water conservation in mind, retrofitting an existing structure to incorporate an RWH system is an excellent option. But before diving into a retrofit, there are several key factors, design criteria, and best practices to consider.

 

Why Retrofit a Commercial Building with a Rainwater Harvesting System?

Rainwater harvesting provides many benefits to commercial buildings, including:

• Water conservation: Helps reduce reliance on municipal water supplies for non-potable uses like irrigation, cooling systems, and toilets.
• Cost savings: By harvesting rainwater, businesses can significantly lower water bills, especially in regions with high water costs.
• Sustainability: Rainwater harvesting supports corporate sustainability goals by reducing the environmental footprint of water usage.
• Regulatory compliance: In some areas, building codes and local regulations encourage or even require rainwater harvesting systems.

However, retrofitting an existing commercial building comes with its own set of challenges. Let’s explore what needs to be considered during the retrofit process.

 

Key Considerations for Rainwater Harvesting Retrofits

1. Roof Size and Condition

• The roof of a commercial building is the primary catchment area for rainwater. Ensure that the roof is large enough to collect a sufficient volume of water to meet your needs.
• The roof’s condition is crucial for system longevity. It must be structurally sound and free of materials that could contaminate the harvested water (e.g., asbestos, bird droppings).
• Roof type: Consider the roof material (metal, asphalt, etc.) as it can affect the water quality and ease of filtration.

2. Local Climate and Rainfall Patterns

• Local rainfall data is essential to determining how much water the system can realistically collect. For regions with limited rainfall, you may need a larger storage capacity or may want to use rainwater for specific applications only (e.g., irrigation or cooling).
• Seasonal variation in rainfall should be factored in. You may need to design the system with more storage capacity to capture water during the rainy season for use during dry periods.

3. Conveyance of Water from Roof to Storage

• Water conveyance systems are the channels and pipes that direct collected rainwater from the roof to the storage tank. Commercial buildings utilize various conveyance systems. It is crucial to design conveyance for necessary access in the event of maintenance or repair needs. An efficient conveyance system can minimize water loss and ensure smooth water flow during storms, helping to maximize water savings.  

4. Pre-Tank Filtration

• Rainwater is often relatively clean but still requires filtration to remove contaminants such as dirt, debris, and organic matter.
• Pre-filtering the rainwater prior to storage is critical for a higher quality of water post-tank. RMS' WISY Vortex Filters act as a first-flush diversion system that discards the first portion of rainwater (which may contain the highest level of contaminants) and can improve water quality for more efficient downstream treatment.

5. Storage Capacity

• The size of the storage tanks will depend on the building's water demand and available roof area. It’s essential to size the tanks to correctly meet water needs without excessive overflow.
• Consider whether the tanks will be located above or below ground. Underground storage can save space, but it may be more expensive and challenging to install, especially in retrofit situations.
• Maintenance access is an important consideration, so ensure that tanks are easily accessible for cleaning and inspections.

6. Post-Tank Filtration

• If the water is intended for potable use, post-tank advancedfiltration and disinfection methods like ultraviolet (UV) light or ultra-filtration are necessary to meet health and safety standards. Check with your local jurisdiction and health department for regulations.

7. Building Plumbing Integration

• Retrofitting an existing building means integrating the harvested rainwater into the building. This may require updates or modifications to the current infrastructure to handle both municipal water and harvested rainwater. A retrofit may dictate your end use applications.
• Ensure that the harvested rainwater is separated from the potable water system unless it's treated to an approved potable standard. 
• Backflow prevention systems are essential to ensure that rainwater doesn't co-mingle with the public water supply in order to meet local regulations.

8. Local Codes and Regulations

• Before beginning a retrofit project, it’s important to check with local authorities to ensure compliance with building codes and water regulations.
• Some jurisdictions may require permits for retrofitting a rainwater harvesting system, and certain standards must be met for water quality, system installation, and storage.
• Investigate whether any incentives or rebates are available to offset the cost of the retrofit.

 

Design Criteria for an Effective Rainwater Harvesting Retrofit

1. System Durability and Longevity

• Opt for high-quality, durable materials that can withstand harsh weather conditions and the wear-and-tear of constant use. Rainwater harvesting systems should be designed for long-term reliability, minimizing the need for frequent maintenance.

2. Cost-Effectiveness

• Evaluate the upfront cost of retrofitting the building with a rainwater harvesting system, including system components, installation, and maintenance. Compare it against long-term savings on water bills.
• Design the system to optimize cost vs. benefit, ensuring that the savings on water and sustainability goals justify the investment.

3. Integrated Systems

• Some commercial buildings may benefit from integrated systems, where rainwater harvesting is combined with other sustainability features such as greywater recycling, stormwater management, and energy-efficient HVAC systems.

4. Backup Water Supply

• Most systems use both harvested rainwater and municipal water to ensure that the building has a continuous, reliable water supply, especially in areas with variable rainfall. The system can be programmed to switch between the two sources as needed.

5. User-Friendly Control System

• Implement a user-friendly control system to monitor water levels, filtration, and system performance. Some systems offer remote monitoring, which can help facility managers track usage and maintenance needs efficiently.

6. Scalability and Flexibility

• When retrofitting, it’s wise to design a system that can be scaled up if water demand increases in the future. Consider adding extra storage capacity or modular components that can be easily expanded.

7. Aesthetic and Space Considerations

• A retrofit may require creative solutions to hide storage tanks or equipment without impacting the building’s aesthetics. Modular or concealed tank designs can help integrate the system smoothly into the building’s overall design.
• The building’s existing plumbing pipes and fixtures may also require innovative thinking to integrate rainwater into the facility.
• Consider systems that are space-efficient, particularly in urban environments where space may be limited.

 

 

Conclusion

Retrofitting a commercial building with a rainwater harvesting system is an excellent way to reduce water consumption, lower operational costs, and contribute to sustainability goals. By considering roof conditions, local climate, water quality, system design, and regulations, businesses can successfully implement a rainwater harvesting system that meets their needs and complies with local codes. With thoughtful planning and the right design, retrofitting your building with a rainwater harvesting system will not only provide long-term environmental and financial benefits but also enhance your building’s reputation as a forward-thinking, sustainable business.

 

Ready to Retrofit?

If you're considering a rainwater harvesting retrofit for your commercial property, our team of experts can guide you through the process—from design to installation. Contact us today to learn how we can help you save water and money!