Managing water hygiene in buildings with RAAC construction

Published: 4-Dec-2023

A crucial guide by Water Hygiene Centre's Roy Sullivan on RAAC construction in unoccupied Buildings

In a significant turn of events for the construction industry, 2023 witnessed a breaking news story surrounding Reinforced Autoclaved Aeriated Concrete (RAAC). Once a widely used construction method, RAAC's resurgence in headlines stems from its potential structural issues, leading to closures of many buildings, particularly schools. This article delves into the reasons behind RAAC's popularity, its pitfalls, and the water hygiene consequences associated with its use.

Why RAAC was used

RAAC gained popularity for being a cost-effective alternative with good thermal insulation qualities and lightweight properties. However, hindsight reveals a critical flaw – insufficient coverage of steel reinforcing bars, leading to exposure and corrosion, jeopardising the structural integrity of buildings.

Water hygiene consequences of RAAC

The closure of buildings constructed with RAAC poses a significant risk to water hygiene. When buildings are unoccupied, the hot and cold-water systems become stagnant, creating a breeding ground for Legionella and other waterborne pathogens. This necessitates proactive water hygiene management to mitigate potential health hazards.

Guidelines for water system management

Referencing HSG 274 – Part 2 section 2.50 – 2.52, the article highlights the importance of managing water systems in mothballed buildings. It emphasises the need for a balanced approach to control microbial growth, utilise water for flushing effectively, and prevent system degradation. The recommendation is to keep systems filled with water during mothballing, with thorough flushing, cleaning, and disinfection before recommissioning.

Other Considerations

The article stresses the importance of a calculated and pragmatic approach based on the likelihood of reoccupation. If reoccupation is imminent, systems should be kept live with a legionella flushing regime. For extended closures, various approaches outlined in HSG274 – Part 2 can be considered. The focus is on minimising risks by implementing effective water management strategies.

Temporary Structures and Water Systems

Schools and organisations affected by RAAC-related closures often resort to temporary structures. The article underscores the need for careful water system management in these structures, including a Legionella risk assessment, before occupation. It references HSG274 – Part 2 – Sections 2.40 – 2.43 for guidance on commissioning requirements.


The Health & Safety at Work Act 1974 places a duty on those responsible for workplaces to ensure premises, plant, and machinery do not endanger people. This duty extends to managing water systems effectively to reduce the risk of incidents related to Legionella and other waterborne pathogens. The article concludes with a reminder that a relatively simple regime can drastically minimise these risks.

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