Why do shower hoses pose a potential Legionella, Pseudomonas aeruginosa, non-tuberculous mycobacteria and other waterborne opportunistic pathogens’ infection risk for users?

Showering is a well acknowledged infection source for waterborne pathogens such as  Legionella, Pseudomonas aeruginosa, non-tuberculous mycobacteria in shower hoses and shower heads (see blog from September 20th, 2021).

Shower hoses are mostly made of plastic, which is organic material and consists mainly of carbon. Carbon and organic materials in general provide excellent nutrient sources for waterborne microorganisms (bacteria, fungi, protozoa). Waterborne microorganisms such as Legionella, Pseudomonas aeruginosa, non-tuberculous mycobacteria, Aspergillus spp., Cryptosporidium, grow based on nutrient availability (food), at ambient temperatures (around 37 °C), and water stagnation (lack of flow).

Shower hoses often contain stagnating warm (20 – 40 °C) water, when not in use. The combination of shower hose materials, these temperatures and water stagnation rapidly contribute (within hours) to biofilm formation. Biofilm is a slimy microbial community (1), on each solid – water interphase and provides mechanical stability to the microorganisms within. Microorganisms within biofilms are protected from chemical, thermal and mechanical stress and have enough nutrients to survive and grow.

Statistics of the past 15 years described in Residential End Uses of Water Study published in 2016 (REU 2016) have shown that showering frequency has remained the same with an average of 1.8 showers per household per day and a duration of 7.8 minutes per shower (2).

 REU* 1999REU* 2016
Sample size (houses)1187762
Average people per household2.82.7
Average showers per household per day1.81.8
Average shower volume (L)63.2 ± 1.159.8 ± 1,9
Average shower duration (min)7.8 ± 0.147.8 ± 0.02
Average flow rate for showers (L/min)8.3 ± 0.157,9 ± 0.15

* Residential End Uses of Water Study (1999 / 2016). Adapted from DeOreo et al., 2016

Additionally, the report confirms that commonly used equipment and set-ups, including hot water recirculating systems and high efficiency showerheads have led to a further reduction of residential indoor water use (2).

A recent global study which included 78 domestic shower hoses, across 11 countries and 3 continents found various inorganic mineral deposits, while 64 shower hoses (82 %) contained Mycobacterium avium, 43 (55%) were colonised with Legionella pneumophila, and 34 hoses (44 %) presented with Pseudomonas. This study goes on to state that 13 hoses that were tested (17 %) were shown to be positive for all three bacteria (Proctor et al., 2018). The authors confirm that biofilm density tends to be higher on shower hoses than on hard pipe materials typically used in building drinking water plumbing (Copper and PEX pipes) and that they were found to additionally host fungi and amoebae. Moreover, as carbon leaching from shower hoses diminishes over time resulting in a nutrient-rich environment in new hoses, and a nutrient-poor environment in old hoses respectively, a stronger biofilm growth is expected in new shower hoses than in old ones (3).

Shower hoses offer excellent growth conditions for waterborne microorganisms as they allow stagnation, appropriate temperature and nutrients availability for biofilm growth. Regular (eg quarterly) cleaning and disinfecting of shower heads and shower hoses has been recommended by UK guidelines to reduce transmission risk to users. However, it is important to weigh the risk of using chemicals: Use of disinfectants may reduce risk from some potential pathogens while increasing risks from others (3).

In summary, water safety groups, landlords, duty holders and responsible people should give careful consideration to the following points for shower hose management:

  1. Do fixed shower head designs offer a reduced risk profile versus flexible hose variants?
  2. What is the appropriate length of a hose to minimise stagnation?
  3. Does a certified shower hose / a shower hose with bacteriostatic additives lead to lower colonisation risk?
  4. In some countries hanging down the shower head to drain out the water is common practice. Is such a process safer?
  5. Is regular dismantling, cleaning, descaling and disinfecting enough to minimize the risk of colonization? Will disinfection and cleaning remove established biofilms within shower hoses?
  6. Should we rethink the number of en-suite and shower facilities required within an existing or new building facility? How does a surplus of showers impact on turnover, flow, and usage of the outlets that remain?

To discuss further, or if you wish to learn more on this and other related topics, please do not hesitate to contact the team directly here.

(1) Flemming et al., „Biofilms: An emerging form of bacterial life“, Nature Reviews Microbiology, 14:563, 2016

(2) DeOreo et al., „Residential End Uses of Water Version 2“, Water Research Foundation, 2016, https://www.redwoodenergy.tech/wp-content/uploads/2017/07/4309B-June-16-2016.pdf accessed on January 15th, 2022

(3) Proctor et al, „Biofilms in shower hoses“, Water Research, 131:274-286, 2018

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