The Importance of water reuse in the UK - Rainwater Harvesting

The Importance of water reuse in the UK - Rainwater Harvesting

As the UK faces growing concerns over water scarcity, flooding, and stricter sustainability standards, rainwater harvesting—a form of water reuse—is rapidly becoming a necessity rather than an eco-friendly option. This essential water-saving solution helps conserve water, reduce flooding risks, and meet evolving planning regulations.

Rainwater harvesting is the collection and storage of rainwater from rooftops, used for non-potable needs like garden irrigation, toilet flushing, and laundry. As water shortages grow across parts of the UK, particularly in the south, harvesting rainwater has become an effective water reuse strategy that minimises reliance on mains water.

With climate change and urban development straining water resources, rainwater harvesting has shifted from a “nice-to-have” feature to a sustainable water management necessity for UK homes.

A rainwater harvesting system typically includes components such as gutters, downpipes, filters, a storage tank, and a distribution network. The system collects rainwater from roofs and surfaces, directs it through filters to remove debris and contaminants, and stores the water for future use.

Some of the most common ways in which harvested rainwater can be reused include:

-Flushing toilets

-Garden use domestically

-Irrigation systems in commercial settings

How a Rainwater Harvesting System Works

Collection

Rainwater is collected from the building's roof, which is ideal due to its minimal debris and contaminants. Water is transported through downpipes and sealed gullies, ensuring no cross-contamination from surface water. Pitched roofs with smooth surfaces are optimal, though rainwater harvesting is suitable for most roof types, including green roofs. Additional filtration is required when collecting from paved or hard-standing areas due to higher pollutant loads.

Preliminary Filtration

Before entering the main storage tank, rainwater passes through a pre-tank filter to remove undissolved solids such as leaves and organic matter. Pre-tank filters use a mesh to capture debris and must be easily accessible for regular cleaning.

Storage

Filtered rainwater is stored in tanks, either above or below ground. Water enters the tank through an inlet calmer, allowing solids to settle. Submersible pumps work with floating suction filters to draw clean water from the tank. Tanks are sized to hold up to 18 days’ worth of water based on typical rainfall patterns. Overflow is designed to prevent stagnation.

Mains Water Backup

A mains water top-up function ensures the system operates during low rainfall or drought. Larger systems use a header tank, while smaller ones utilise a pressure vessel. This function operates automatically and is controlled by sensors.

Additional Filtration

To optimise performance, additional filtration such as UV disinfection is recommended for vulnerable settings or fine vapour applications. Best practice includes a third filtration stage for internal protection.

Usage Points

From the tank, the water is pumped to the relevant appliances through a floating filter extraction point, which is positioned just below the water surface to ensure the pump draws water that is free from sediment.

Rainwater harvested in the UK is primarily used for non-potable purposes, including:

• Irrigation: Supplying water for gardens, lawns, and agricultural needs.
• Flushing Toilets: Reducing the demand for treated mains water.
• Cleaning: Washing vehicles, windows, and outdoor areas.
• Industrial Uses: In certain industrial processes where potable water is not required.

Rainwater harvesting benefits

• Reduction in mains water usage – saving money
• Complies with BREEAM, LEED, & WRAS requirements
• Energy efficient
• Inert – no use of chemicals
• Flood reduction
• Can be combined with our greywater recycling systems
• Compact and easy to install
• Can accommodate any building due to flexible above or below-ground storage systems

Challenges and Considerations

• Water Quality: As the water collected is typically non-potable, it must be adequately filtered and maintained to avoid contamination, particularly if used for irrigation or cleaning purposes.
• Installation Costs: Initial installation can be costly, though long-term savings may offset this.
• Space Requirements: Storage tanks require adequate space for installation, which can be a limitation in urban settings.

Regulations and Standards

Regulations and Standards: In the UK, rainwater harvesting systems must comply with relevant regulations to ensure safety, efficiency, and effectiveness. Notable standards include:

BS 8515:2009+A1:2013: This code of practice outlines the installation, maintenance, testing, and quality control of rainwater harvesting systems, ensuring they are fit for non-potable water use.

Water Supply (Water Fittings) Regulations 1999: These regulations govern the use of rainwater harvesting systems for internal applications, ensuring they meet hygiene and safety standards.

In conclusion, rainwater harvesting presents a viable solution for enhancing water conservation efforts in the UK, promoting sustainability while supporting water usage efficiency. Proper design, installation, and maintenance of systems are essential to ensure their reliability and effectiveness.

By Paulina Stanislawczyk MSc CEng MCIBSE ASoPHE