Water systems in healthcare settings are complex and vulnerable to contamination by opportunistic waterborne pathogens such as Pseudomonas aeruginosa, Legionella pneumophila, and non-tuberculous mycobacteria (NTM). These pathogens can cause severe infections, particularly in immunocompromised or critically ill patients. Infection Prevention and Control (IPC) teams often rely on point-of-use (POU) filters at taps and showers as a barrier method. However, there are many situations where POU filters are not feasible due to design, safety, or practical limitations. In these cases, in-line filters (installed within the plumbing system upstream of the outlet) can be an effective alternative. Though they do not offer the same level of protection as POU filters in high-risk areas, they play a vital role in a risk-based water safety strategy.
POU filters are devices fitted directly to taps, showers, or other outlets at the water delivery point. POU filters are usually attached onto the outlet itself and provide immediate protection by preventing bacteria from passing into the water stream used by patients. In-line filters serve the same purpose but are installed within the plumbing supply line upstream of the outlet or device. Instead of attaching to the outlet directly, an in-line filter cartridge might be placed behind a wall panel, above a ceiling, or inside equipment – anywhere “in line” with the water pipework.
While POU filters remain a highly effective and widely used intervention, their utility may be limited in certain situations due to outlet design, user interaction, or specific environmental needs. In-line filters offer distinct advantages in such cases:
Mental health environments demand fixtures that minimize the risk of harm by using anti-ligature outlets. These often have concealed or custom-designed nozzles, making it impossible or inappropriate to attach external filters as this may conflict with anti-ligature design standards. In-line filters avoid this by remaining hidden behind wall panels, cavities, or ceiling voids, eliminating exposed components, and maintaining a safe and compliant environment.
Medical devices such as dental units, autoclaves, endoscope washers, and ice machines use water internally, making POU filters unsuitable. In-line filters, positioned before or within these units, ensure incoming water meets microbial safety standards, reducing the risk of biofilm growth and equipment contamination.
In lower-risk settings where appearance, tampering, or frequent user access is a concern (such as outpatient clinics or public-facing areas), POU filters may be prone to damage or misuse. In-line filters offer an invisible, tamper-proof alternative with longer service life and minimal patient interaction.
In-line filters can be used in various applications across healthcare estates. Some key use cases include:
In-line filters can be highly effective at removing waterborne pathogens like Legionella and Pseudomonas from the incoming water supply. However, compared to traditional POU filters, one critical limitation is the risk of post-filtration (after-filter) microbial contamination in the pipework between the filter and the outlet.
When an in-line filter is installed upstream of the final outlet (e.g., within ceiling voids or behind walls), the water still travels through a short length of pipework before reaching the user. This downstream section is unprotected by the filter and can become colonized with bacteria over time – especially if conditions promote biofilm formation, such as:
The pathogens growing in this after-filter pipework can be released intermittently during use, bypassing the filtration barrier and exposing patients. To mitigate this, it is essential to install the in-line filter as close to the outlet as possible, minimizing the length of unprotected pipe.
Where short connections are unavoidable, the use of smooth-bore, rigid, or antimicrobial pipe materials can reduce biofilm risk. Regular thermal or chemical disinfection of downstream pipework should also be considered, especially in areas with stagnant water or infrequent use. Daily flushing routines and careful configuration of thermostatic mixing valves (ideally located before the filter) further support control.
In-line filtration offers an essential tool for controlling waterborne pathogens in healthcare environments, especially where traditional point-of-use filters are impractical or incompatible. By enabling safe water delivery to various outlets and devices without disrupting existing infrastructure or creating ligature risks, these filters help estates and IPC teams maintain compliance and reduce infection risk in complex healthcare estates.
However, while in-line filters offer discrete and flexible protection against waterborne pathogens, they do not protect the outlet from after-filter contamination. Unlike traditional POU filters fitted directly to taps or showers, in-line filters rely more heavily on installation design and maintenance practices. Estates and IPC teams should document these arrangements in the facility’s Water Safety Plan and ensure regular monitoring to confirm ongoing protection.
Explore how the Chrome In-Line Filter supports infection prevention with a clinically focused, evidence-based design.
