It has been found that the internal supports in cold water tanks can hold stagnant water that can allow biofilm and slime growth which can harbour micro-organisms such as Legionella and Pseudomonas. The use of uncapped PVC-U pipes (or similar) within cold water tanks as a support structure for the lid is likely to lead to stagnation and harbouring of harmful micro-organisms.
The UK Department of Health Alert (EFA/2013/004) issued on 19th November 2013, has highlighted an issue with cold water storage tanks which indicates that hollow tank supports are no longer permitted in cold water storage tank installations. This is also supported by the new ACoP L8 legislation provided by the Health and Safety Executive.
Hollow internal supports restrict the movement of water, allowing bacteria to form within a cold water storage tanks. Tanks that contain hollow supports have been identified by the HSE and EFA as providing an environment in which water can stagnate. The presence of stagnant water is likely to encourage the growth of Legionella bacteria above the recommended risk levels. This would then present the risk of the entire domestic water system becoming contaminated. The Hollow Supports should be removed to eliminate possible contamination and replaced with ‘clean’ solid supports, i.e. ones without cavities, crevices or details allowing water to stagnate and harbour micro-organisms.