Drinking water safety in haematology units: an under‑recognised infection risk?

I've put together this blog in preparation for today's Insight Webinar with Dr Jessica Martin, all about water hygiene!

Water systems are a recognised source of healthcare associated infection, particularly in augmented care settings. IPC attention has traditionally focused on sinks, drains, and showers, yet far less scrutiny has been given to a routine exposure: the water patients are encouraged to drink.

A recent research letter in the British Journal of Heamotology  questions whether current approaches to drinking water provision for haematopoietic stem cell transplant (HSCT) patients are sufficiently evidence‑based, consistent, and risk‑informed.

Why ingestion matters

HSCT recipients are highly susceptible to opportunistic waterborne pathogens, including Pseudomonas aeruginosa, non‑tuberculous mycobacteria, and Stenotrophomonas maltophilia. While inhalation and contact routes are well recognised, ingestion is also a relevant route of exposure in immunocompromised patients.

The paper also highlights the potential interaction between drinking water and the gut microbiome, increasingly linked to transplant outcomes. Despite this, the clinical impact of healthcare acquired waterborne organisms on gut microbial diversity remains poorly understood.

Drinking water therefore intersects infection risk, antimicrobial resistance, and host susceptibility, yet is rarely considered explicitly within IPC risk assessments.

Variation in practice reflects uncertainty

In the absence of clear national guidance, the authors surveyed UK allogeneic HSCT centres and identified marked variation in practice, including:

• Unfiltered tap water
• Filtered tap water, often with unclear sterilising performance
• Cooled boiled water
• Bottled water

Post‑discharge advice was similarly inconsistent, most commonly recommending tap water.

No centres reported confirmed waterborne infections. However, the authors emphasise that current surveillance systems are poorly suited to detecting sporadic, ingestion‑related transmission, particularly outside outbreak settings. Absence of reported infection should not be interpreted as evidence of safety.

Surveillance limitations and false reassurance

Routine water monitoring typically focuses on Legionella spp. and P. aeruginosa, often using infrequent sampling. While appropriate for system level assurance, this may provide false reassurance for highly immunocompromised patients.

Low‑level contamination, biofilm persistence, and delayed presentation limit the sensitivity of standard surveillance models, raising the question of whether population level water standards adequately protect high‑risk groups.

Beyond the tap: the drinking water pathway

A key contribution of the paper is its focus on the entire drinking water pathway, rather than water quality alone. Risks may arise from:

• Outlets near sinks and wastewater sources
• Storage vessels such as jugs and cups
• Preparation and handling practices
• Re‑contamination during cooling or delivery

Even established mitigations, such as cooled boiled water, introduce additional risks, including staff workload, scald injury, poor palatability, reduced intake, and opportunities for contamination.

Implications for IPC

While the authors stop short of prescriptive guidance, their findings have several important implications for IPC teams:

• Drinking water should be explicitly included in IPC risk assessments for HSCT and other highly immunocompromised patients.
• Variation in practice reflects unresolved risk, rather than local optimisation.
• Routine surveillance may not detect clinically relevant exposure, reinforcing the need for precautionary, risk‑based approaches.
• Engineering controls, such as dedicated drinking water outlets with sterilising‑grade filtration away from sinks, may reduce risk but require careful consideration of feasibility and sustainability.
• End‑to‑end pathways matter, including storage, handling, and patient delivery, not just outlet water quality.

These findings support a move away from ad‑hoc local solutions towards coordinated, multidisciplinary decision‑making.