52
feature
drainage, plumbing & water saving solutions
decarbonisation and green energy
– the impact on water safety Andy Clews, Senior Consultant at Water Hygiene Centre, discusses the hidden legionella risks associated with lower operating temperatures, the challenges of rainwater harvesting and greywater systems, and practical strategies to balance sustainability with compliance and public health...
Decarbonisation and green energy measures can have a major effect on water safety in buildings. Although they reduce carbon emissions, they may also create serious unintended risks, including increased growth of Legionella and other opportunistic pathogens caused by system stagnation, lower water temperatures, and reduced disinfectant residuals. Core risk factors Lower operating temperatures: Choosing heat pumps to be the primary heat source should be carefully managed if hot water at 60°C is to be achieved. The pasteurisation requirement should not be overlooked thus 70°C should be achievable. Heat pump performance varies with ambient conditions, a building’s actual heat demand, operating temperatures and with age, so optimising
the heat pump benefits may require supplementary plant and equipment. Reducing hot water storage temperatures
may appear to be a simple way to cut energy use, but it involves more than adjusting the hot water generator set point. Lower temperatures can allow water to fall within the ideal growth range for Legionella bacteria. ACoP L8 requires hot water to be stored at 60oC and delivered at 50oC at outlets, or 55°C in healthcare settings. Alternative control measures may be acceptable where a competent Legionella risk assessment or design review demonstrates that they are equivalent to, or better than, the ACoP L8 requirements. Low-flow fixtures: Retrofitting existing plumbing with water-saving fittings, such as aerators,
low-flow showerheads and dual-flush cisterns, can reduce water use but may also cause pressure drops, flow imbalance and blockages in domestic water and drainage systems. Reduced flow rates lower water velocity and shear stress, allowing biofilms to develop and sediment to accumulate, which can increase maintenance requirements and affect system reliability. Existing drainage systems are often sized
for larger-volume cisterns, so replacing them with low-volume dual-flush units may provide insufficient water to clear waste effectively. This can lead to repeated flushing, which undermines the intended water savings. Cold water storage: Storage calculations sometimes include allowances for future expansion, and tanks may be selected at the next size above
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