DRAINAGE & PLUMBING “
Harvesting rainwater not only minimises our dependence on increasingly costly water from the mains (reducing usage by between 40 and 50%), but an efficient RWH tank will also make a huge difference to the end-user’s bill.
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manufacturers for advice if in any doubt at all.” Whilst collecting excess rainwater and retaining it for reuse does provide an extra element of security against flooding, it can’t replace or match the benefits of an entire sustainable urban drainage system (SuDS). This is where two-in-one RWH and SWM systems come in – providing both effective flood prevention, matched with a sustainable way to re-use water Rolfe adds.
rainwater in an underground tank, which is then pumped directly to the points of use as and when water is needed (e.g. when a tap is turned on, or valves on toilets are opened). In some systems, this pump is submersed in the tank, whereas in others (such as GRAF UK’s ECO-Plus system with the Platin tank), it is built into a sperate controls unit, which keeps the technology dry and protected from the elements. • Indirect systems also collect water in an underground storage tank, but it is then pumped to a header tank, which is often situated in a property’s roof space. In turn, this tank gravity- feeds the harvested water directly to the point of use. This means indirect systems have much simpler controls than direct ones – if any at all. For example, they are typically set so that the header tank holds enough water to last for around three or four flushes of a toilet. Only then is the pump in the underground storage tank activated to replenish it (saving energy in the process). • Above-ground (or gravity-fed tanks) are the most energy-efficient RWH option. However, they are especially suited to larger commercial buildings with significant roof space and substantial structural support where water demand is minimal (e.g. warehouses). In this case, the surface area of the roof is used to
harvest the rainwater, which is fed directly into a large header tank. The water is then simply gravity-fed to the points of use.
Specifying for success “As well having a strong knowledge of the products on the market, it’s also helpful for merchants to be aware of other factors that come into play at the RWH specification stage” Rolfe says.
“This includes determining the property type and establishing what the harvested water is going to be used for. When it comes to working out the capacity of the tank, the property’s size (including its roof area) and the number of residents will form a key part of the equation. At GRAF UK we would always recommend asking
December 2018
www.buildersmerchantsjournal.net
Effective water management Not only does combining the two functions make it more cost-effective, incorporating SWM means projects can comply with strict water run-off requirements set by local environment authorities, as well as guidelines set out by the Flood and Water Management Act of 2010. This ensures effective surface drainage is part of all new development plans. Rolfe explains that Stormwater attenuation can be incorporated into a RWH system with a one-tank solution, while infiltration will generally require a separate system. For larger-scale projects, attenuation tanks can be designed from modular cells wrapped in an LLDPE-welded membrane (such as GRAF UK’s EcoBloc range). The outflow rate is regulated to allow the water above the outlet to be discharged into the sewage system in a controlled manner, whilst the water below the outlet, at the bottom of the tank, is retained for reuse.
The opportunity
Ultimately, merchants who arm themselves with the right knowledge are in pole position to reap the rewards of what’s becoming an increasingly booming water management market. Those who can offer both effective and compliant systems will be able to deliver the very best results for customers, both now and well into the future. BMJ
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