High-Risk Water System Components: Showers, Outlets and Terminal Fittings

Flexible Hoses: Technical Considerations for Water Hygiene and Legionella Risk Management

In accordance with HSG274 Part 2, Section 2.31, the use of flexible hoses in domestic water systems presents a recognised risk factor for Legionella proliferation, particularly when hoses are of poor construction quality or installed inappropriately. Section 2.31 explicitly advises against the use of non-smooth bore, non-WRAS-approved hoses, as these can support biofilm formation, retain stagnant water, and compromise system integrity. Corrugated internal surfaces and substandard materials exacerbate microbial colonisation, increasing the risk of Legionella amplification.

From a healthcare perspective, HTM 04-01 reinforces the requirement for all water systems—particularly those supplying augmented care areas—to be designed and maintained to inhibit microbial growth. The document stipulates that flexible hoses should only be installed where their use is unavoidable, and when installed, must meet stringent performance criteria:

Constructed from WRAS-approved, smooth-bore materials

Kept as short as practicable

Installed to permit full drainage and avoid kinks, loops, or dead legs

Moreover, hoses must be identified within the water system schematics and included in the asset register for the purposes of risk assessment, maintenance scheduling, and compliance monitoring. As part of the Water Safety Plan (WSP), flexible hoses should be subjected to routine inspection, with a documented replacement frequency based on manufacturer recommendations and risk profile.

Operators and Responsible Persons must ensure that flexible hoses are incorporated into the ongoing microbiological monitoring programme and remain compliant with the Approved Code of Practice (L8). Any deviation from the recommended standards should be justified within the site-specific risk assessment, and subject to validation and review by the Water Safety Group (WSG) where applicable.

In addition to flexible hoses, certain terminal fittings and components in water systems—particularly in healthcare and high-occupancy environments—present significant risk factors for the harbourage and proliferation of Legionella bacteria, especially when poorly maintained or inadequately specified.

Multi-Spray Pattern Showerheads

As outlined in HSG274 Part 2 (Sections 2.37–2.41), showerheads and particularly those with multi-spray or adjustable settings are considered high risk due to:

• The complex internal design that facilitates water retention
• Increased surface area promoting biofilm formation
• A high potential for aerosol generation, which is the primary route of Legionella transmission

HTM 04-01 advises that only simple, single-spray showerheads should be used in healthcare settings, and they must be designed to permit full disassembly and cleaning. Where multi-spray heads are present (e.g., in legacy installations), they should be replaced or supported by robust decontamination procedures, including weekly flushing, quarterly descale and disinfection, and more frequent regimes based on local risk assessments.

Thermostatic Mixing Valves (TMVs)

TMVs are required for scald protection but represent a critical risk point for microbial growth due to:

• Warm blended water stagnating in downstream pipework
• Infrequent use leading to low turnover
• Accumulated scale or organic matter in the mixing chamber

Both HTM 04-01 and HSG274 Part 2 (Section 2.20–2.25) mandate that TMVs be installed as close to the point of use as practicable and be subject to planned preventative maintenance, including temperature verification, cleaning, and functional testing at defined intervals.

Taps with Flow Straighteners or Aerators

Outlets fitted with aerators or flow straighteners can present increased risk unless carefully managed. These fittings can:

• Trap debris and biofilm
• Reduce turbulence, leading to partial stagnation
• Interfere with effective flushing

HTM 04-01 recommends the removal of aerators unless they are essential for clinical or operational reasons. Where they remain in use, they must be included in the cleaning and disinfection regime, with the frequency determined by local microbiological monitoring data.

Summary of Control Measures

• Eliminate or replace high-risk fittings where possible
• Specify WRAS-compliant, low-risk components
• Implement enhanced cleaning and disinfection schedules
• Incorporate all fittings into schematics, asset registers, and WSP documentation

Undertake regular condition checks, temperature profiling, and microbial sampling in accordance with HTM 04-01 Part B and HSG274 Part 2

Written by Carl Ollerton – Technical Director – GMS Services Ltd