---
title: "Non-tuberculous mycobacteria in water systems: why Legionella controls are not enough"
source_url: https://legionella.io/articles/non-tuberculous-mycobacteria-in-water-systems-why-legionella-controls-are-not-enough/
canonical_url: https://legionella.io/articles/non-tuberculous-mycobacteria-in-water-systems-why-legionella-controls-are-not-enough/
pillar: "Legionella Basics & Science"
summary: "Non-tuberculous mycobacteria tolerate heat and chlorine, so the controls that beat Legionella do not reliably clear them. What NTM are and why they matter."
primary_keyword: "non-tuberculous mycobacteria in water systems"
date_published: 2026-06-27
date_reviewed: 2026-06-27
author: "Legionella.io editorial team (REMOTE TECH LTD)"
reviewed_against: "HSE L8 and HSG274 guidance"
region: "United Kingdom"
license: "CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Quote, adapt or republish with attribution to REMOTE TECH LTD and a link to source_url."
license_url: https://creativecommons.org/licenses/by/4.0/
---

# Non-tuberculous mycobacteria in water systems: why Legionella controls are not enough

Most building water safety programmes are built around one organism. Temperature control, flushing and the occasional disinfection are all aimed at keeping *Legionella* in check, and for that job they work well. The trouble is that a clean Legionella result does not certify the whole water system as safe. Other waterborne organisms live in the same pipes and biofilm, and some of them shrug off the very conditions that control Legionella. Non-tuberculous mycobacteria, usually shortened to NTM, are the clearest example.

This article is general background for estates and infection-prevention readers, not medical advice. Any concern about illness should go to a clinician or the relevant NHS service.

## What non-tuberculous mycobacteria are

"Non-tuberculous mycobacteria" is a broad label for the *Mycobacterium* species that are not the cause of tuberculosis or leprosy. They are environmental organisms: commonly found in soil, natural water and the engineered water systems inside buildings [2]. Unlike Legionella, which has to be amplified inside a building system before it reaches risky numbers, many NTM are simply part of the background flora that arrives with the mains supply and settles in.

Two features make them awkward for water safety. First, they have a waxy, lipid-rich cell wall, which is part of why they are comparatively tolerant of disinfectants and of heat compared with many other waterborne bacteria [2]. Second, they are strongly associated with biofilm, the slimy microbial layer that coats the inside of pipes, tanks, taps and fittings [2]. Biofilm shelters organisms from both temperature swings and chemical dosing, so a pathogen that favours biofilm is, by design, hard to reach with the usual tools.

## Why Legionella controls do not reliably remove them

The standard Legionella regime leans on two levers: keep hot water hot, keep cold water cold, and where needed apply a disinfectant such as chlorine. Legionella is sensitive to sustained heat, which is the principle behind [thermal disinfection using heat to control Legionella](https://legionella.io/articles/thermal-disinfection-using-heat-to-control-legionella/). NTM do not respond in the same way. Reported evidence indicates they are typically more heat-tolerant and more chlorine-tolerant than Legionella, which means a hot-water temperature or a chlorine residual that suppresses Legionella may leave NTM populations largely intact [2].

There is an uncomfortable second-order effect. Some NTM are reported to persist, and in places appear to be favoured, in warmed water and in systems where competing organisms have been knocked back. This is why treating "Legionella is controlled" as "the water is microbiologically safe" is the wrong inference. The differences between Legionella and other organisms are explored further in [Legionella versus other waterborne bacteria](https://legionella.io/articles/legionella-vs-other-waterborne-bacteria-key-differences/).

## Myth versus reality

**Myth: "If my Legionella controls are good, the water is safe."**

This is the assumption most worth challenging. A well-run temperature and monitoring regime genuinely reduces Legionella risk, and it should not be abandoned. But it is a control for one organism, not a guarantee for all of them.

**Reality: some pathogens persist despite good Legionella control.**

NTM are environmentally common, biofilm-associated and comparatively tolerant of the heat and chlorine that control Legionella [2]. That combination means a system can return reassuring Legionella results while still carrying NTM in its biofilm. The practical conclusion is not panic and it is not abandoning temperature control. It is recognising the limits of a single-organism strategy, and, where vulnerable people are exposed, assessing for pathogens beyond Legionella as well. Risk assessment standards already point this way: BS 8580-2 covers waterborne pathogens beyond Legionella, NTM among them, and sets out how to assess them [1].

## Where NTM actually matter

For the great majority of ordinary buildings, NTM are a background presence rather than a pressing hazard. They become a genuine concern where two things line up: a susceptible population, and a route by which the organism reaches them. That is overwhelmingly a healthcare picture rather than a general office one.

In healthcare, the relevance is recognised in NHS England guidance on safe water, which addresses *Mycobacterium* species in water and the augmented-care settings where extra precautions apply [3]. Augmented care covers areas where patients are particularly vulnerable, for example because they are severely immunocompromised or have invasive devices. In those settings the response can include point-of-use filtration at outlets and tighter scrutiny of water quality, because the consequence of exposure is far higher than in a general ward [3]. A widely discussed line of cases has also linked certain *Mycobacterium* species to specialised medical devices that aerosolise water, which is why device-specific water management sits alongside the building water system in clinical risk thinking [3].

The general principle for duty holders is the same one that already governs Legionella: match the rigour of control to the vulnerability of the people exposed. A care setting, a dialysis unit or an augmented-care ward warrants a wider lens than a low-occupancy commercial office.

## What a duty holder should take from this

You do not need to redesign your whole programme around NTM. You do need to stop treating Legionella control as a proxy for total water safety. A few practical positions follow from that.

- Keep your temperature and monitoring regime running. It controls Legionella and it remains the foundation [2].
- Recognise that heat and chlorine at Legionella-control levels are not a reliable kill for NTM [2].
- Where the exposed population is vulnerable, ensure the risk assessment considers pathogens beyond Legionella, in line with BS 8580-2 [1].
- In healthcare and augmented care, follow NHS England water-safety guidance, including point-of-use measures where indicated [3].
- Manage biofilm and stagnation, since these favour a range of waterborne organisms, not Legionella alone [2].

NTM are not the only organism in this category. Pseudomonas is another that warrants attention in vulnerable settings, covered in [Pseudomonas aeruginosa in water systems](https://legionella.io/articles/pseudomonas-aeruginosa-water/), and the wider picture is set out in [Legionella and other pathogens in building water systems](https://legionella.io/articles/legionella-and-other-pathogens-in-building-water-systems/). The thread running through all of them is the same: a water system is an ecosystem, and controlling its best-known inhabitant is necessary but not sufficient.

## Frequently asked questions

### Do my Legionella controls also kill mycobacteria?

Not reliably. The heat and chlorine levels used to control Legionella are reported to be less effective against non-tuberculous mycobacteria, which are comparatively tolerant of both and which shelter in biofilm [2]. A good Legionella result does not confirm that NTM are absent or controlled. Keep your Legionella regime running, but do not treat it as a guarantee for every organism.

### Where are non-tuberculous mycobacteria a problem?

They are most relevant where vulnerable people are exposed, which in practice means healthcare and augmented-care settings rather than ordinary buildings [3]. NHS England guidance addresses *Mycobacterium* species in water and the precautions, including point-of-use filtration, that may apply in those areas [3]. In a typical low-risk office, NTM are usually a background presence rather than a pressing hazard.

### Does chlorination remove NTM from a water system?

Chlorination is a core tool against Legionella, but reported evidence indicates NTM are comparatively chlorine-tolerant, partly because of their waxy cell wall and their association with biofilm [2]. Routine residual chlorine levels should not be assumed to clear them. This is one reason BS 8580-2 sets out assessment for waterborne pathogens beyond Legionella [1].

### Should a normal office worry about NTM?

For most general-occupancy buildings the day-to-day NTM risk is low, and a sound Legionella programme that also limits biofilm and stagnation is a reasonable position [2]. The picture changes where susceptible people are present, where a wider risk assessment is appropriate [1]. This is general information and not medical advice; route any health concern to a clinician or NHS service.

## Sources

[1] BSI, BS 8580-2:2022, code of practice for risk assessments for *Pseudomonas aeruginosa* and other waterborne pathogens (non-tuberculous mycobacteria as a covered pathogen and the assessment approach). https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-pseudomonas-aeruginosa-and-other-waterborne-pathogens-code-of-practice

[2] CDC, About Legionella and related waterborne pathogens guidance (environmental occurrence, biofilm association and relative tolerance of chlorine and heat). https://www.cdc.gov/legionella/about/index.html

[3] NHS England, HTM 04-01: Safe water in healthcare premises (relevance of *Mycobacterium* species in water and augmented-care precautions). https://www.england.nhs.uk/publication/safe-water-in-healthcare-premises-htm-04-01/