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Building Products March 2018

DRAINAGE, PLUMBING AND WATER SUPPLY <<< Continued from page 47 from components that would otherwise be supplied using potable water (e.g. industrial cooling systems, toilets, dishwashers, etc). Rainwater should only be used for irrigation and landscaping, once that demand has been satisfied. Perhaps even more compelling than the environmental reasons driving interest in RWH, is the strong financial case it presents. RWH systems can help cut bills by reducing reliance on costly drinking-quality water from the mains wherever it’s not absolutely necessary (e.g. for toilet flushing and washing machines). In fact, the most efficient systems can reduce mains water usage by between 40% and 50% – a substantial saving which is set to grow even further as water companies put prices up to cope with the surge in population. The larger the building and the higher its water usage, the more economic sense a RWH system will make. The payback period of installing a largescale commercial RWH system is usually between three and five years, and with additional tax incentives available to encourage investment in water-saving technologies, the attraction is hard to miss. The commercial RWH market at glance When it comes to choosing the right RWH system for a project, commercial specifiers have three main options to choose from. Direct systems are the most common RWH option for commercial applications. They collect water in an underground storage tank, which is then pumped directly to the point(s) of use when the water is needed (e.g. when a tap is turned on, or when the valves on toilets are opened). In some systems, this pump is submersed in the tank, whereas in others it is built in to a controls unit in a separate plant room which keeps the technology dry. For large-scale installations, twin pump sets are typically fitted to ensure continued operation should one malfunction. Above-ground, gravity-fed tanks are the most energy-efficient RWH option. They are especially suited to larger buildings with significant roof space and substantial structural support, where water demand is minimal (e.g. warehouses). In these instances, the surface area of the roof is used 48 BUILDING PRODUCTS | MARCH 2018 not suitable for infiltration. Attenuation can usually be incorporated into a RWH system with a one-tank solution – for instance by using modular cells wrapped in an LLDPE-welded membrane. The top part of the tank is used for attenuation, whilst the remainder is retained for re-use. The legislative context Last but not least, those specifying commercial RWH and SuDS systems should have a good grasp of the official guidelines governing the sector. The Flood and Water Management Act of 2010, for example, was introduced to provide more comprehensive management of flood risk for commercial properties and homes alike. It aims to develop better resilience to climate change following the widespread flooding of 2007, notably by requiring the inclusion of sustainable drainage of surface water in construction. The National Flood and Coastal Erosion Risk Management Strategy also outlines the need to appraise and adopt, as appropriate, the full range of measures that may be available to manage the risk of flooding – including using combinations of water storage and SuDS. Specifiers armed with a basic understanding of these guidelines – plus the right product knowledge to boot – can ensure they are specifying both effective and compliant systems for their customers. The future The potential benefits of commercial RWH solutions – especially when combined with SuDS – are much greater than in the case of smaller domestic applications, and the return on investment period is typically a lot shorter. With demand showing no sign of slowing, specifiers who stay abreast of the latest product and legislative developments will be able to truly maximise the opportunity at hand. grafuk.co.uk to harvest the rainwater, which is fed into a large header tank. The water is then simply gravity-fed to the points of use. Combined RWH and stormwater management systems match rainwater harvesting with effective stormwater management for a dual-capability solution, which makes both functions even more cost-effective. These solutions are known as sustainable urban drainage systems (SuDS), and feature one of two methods of stormwater management: • Attenuation, where water is retained and then slowly discharged into the surface water drainage system or water courses. • Infiltration, where water is gradually released back into natural groundwater reserves. While both can be combined with RWH, attenuation is far more common in the UK because the clay-heavy soil in many areas of the country is RWH with stormwater attenuation Indirect RWH system


Building Products March 2018
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