legionella-shower-water-safety-guide

legionella-shower-water-safety-guide

ByKen

As an Amazon Associate we earn from qualifying purchases.

Legionella shower water safety starts with knowing where the bacterium grows. Legionella is a bacterium that grows in water systems, and a household shower is one place it can be found. The question most households ask is practical: who should worry, what routine makes sense, and what the research actually shows. This guide uses three sources: U.S. EPA guidance and two household studies, one from the UK and one from Adelaide, Australia. Both studies are small and observational, and neither measures illness in the people who used the showers.

Quick answer

  • EPA says that people are exposed to Legionella “when they inhale water droplets containing the bacteria”, and it lists premise plumbing, including hot water heaters and pipes in buildings, as places where Legionella can grow.
  • EPA also says that “Most healthy people do not become infected with Legionella after exposure”. It lists people 50 years or older, current or former smokers, people with chronic lung disease, and people with a weakened immune system as the groups at higher risk.
  • In the UK study, 99 showers from 82 properties were sampled. Clinically relevant Legionella was isolated by culture from 8 percent of shower water samples.
  • In the Adelaide study, 68 showers were tested, and 74.6 percent were positive for Legionella spp. by qPCR. The authors associate higher concentrations with higher hot water temperatures and with showers used less often.

What EPA says about the risk

EPA’s Legionella page is the most general source here. It explains that Legionella bacteria “are found naturally in the environment worldwide, usually in aquatic environments”, and that they also occur in distribution systems and premise plumbing. The page lists large buildings, cooling towers, decorative fountains, and hot tubs as places where the bacteria can grow, along with hot water heaters, storage tanks, and pipes in large buildings. It does not list a home shower as a separate category, so the household picture comes from the studies below.

The disease EPA describes is a respiratory illness. It says that the bacteria can infect the lungs and cause a severe pneumonia called Legionnaires’ disease, and that they can also cause a milder illness called Pontiac fever. The page does not give a cure or a home treatment, and this guide does not offer one.

EPA’s advice for a positive household test is brief. It says to consult the state and county health departments, and it says that single-family or small multiple-family residences should follow current state, county, and city guidelines for their water. For a household that has a test result, that is the first call to make.

The UK household shower study

The UK study sampled 99 showers from 82 separate properties in the South of England. The authors used culture and qPCR. They report that “Clinically relevant Legionella spp. were isolated by culture in 8% of shower water samples representing 6% of households”. A further 31 percent of showers were positive by qPCR for Legionella spp. In a multi-variable model, qPCR positivity was linked to the age of the property and the age of the shower, and the frequency of use was borderline.

The study also reports patterns in concentration. The authors write that “The concentration of Legionella spp. detected by qPCR was shown to decrease with increased frequency of use”, and that more frequent showerhead cleaning was linked to lower concentrations. They found “no association between Legionella spp. qPCR positivity and the cold water supply or the showerhead material”. The authors conclude that household showers “may be important reservoirs of clinically significant Legionella and should be considered in source investigations”.

The study’s own summary is cautious. It says that “Simple public health advice may help to mitigate the risk of Legionella exposure in the domestic shower environment”. It does not test a specific advice package, so the advice is a hypothesis for households to weigh against their own circumstances. It is also a sample from one region, and the abstract we checked does not report the number of people who used each shower.

The Adelaide household shower study

The Adelaide study, published in the journal Pathogens in 2019, tested domestic showers across metropolitan Adelaide, South Australia. It used qPCR to count Legionella spp. and L. pneumophila in water samples, and it used a survey to identify risk factors and awareness. The authors report that “A total of 74.6% (50/68) and 64.2% (43/68) showers were positive for Legionella spp. and” L. pneumophila. Both figures come from qPCR, so the study shows the presence of bacterial DNA in the water, which is not the same as a measured number of infectious bacteria.

The authors link higher concentrations to higher hot water temperatures, to showers used at least every week, and to houses less than five years old. They report that showers used less than once a month had higher concentrations than showers used once a week or more often. The study was a single-region survey of a limited number of homes, so the links are associations, not proof of cause.

The authors’ conclusion includes a recommendation that households may find surprising. They state that “Increasing hot water temperature and running showers every week” were identified as strategies to reduce the risk. The idea of running a shower every week to replace the water in pipes is a practical one. The hot water part of the recommendation is different. It conflicts with the 120-degree guidance for scald prevention that the CPSC and other sources give, and our sources do not provide a temperature that addresses both risks. A household that is weighing these two concerns should ask its local health department, as the EPA page advises, before changing a heater setting.

The authors also note “The lack of public awareness in this study” and call for “public health campaigns to inform vulnerable populations of the steps they can take to reduce the risk”. That point matters for this guide because the household is the place where a routine is set.

A practical shower routine from these sources

From the studies, the steps with the most support are modest. Run the shower at least once a week, as the Adelaide authors suggest, so that water that has sat in the pipes is replaced. Clean the showerhead on a regular schedule, since the UK study links more frequent cleaning with lower concentrations. Avoid long periods without use before a shower is run, which is the same principle as the weekly run. Keep the hot water setting within the limits the household has checked with its local guidance, and do not change the heater setting based on one study alone.

If a household member is in one of the higher-risk groups EPA lists, the household should raise the question with a doctor and with the local health department. A household member with a chronic lung disease, a weakened immune system, or a smoking history is in a different position from a healthy adult, and the sources do not give a home screening method.

What we could not verify

  • We did not find a source that gives a safe hot water temperature that balances Legionella control and scald prevention. The Adelaide authors name a higher temperature as a strategy, and the scald guidance names 120 degrees, so this guide does not give a single number.
  • The UK study reports positive results but does not report whether any shower user became ill. The Adelaide study does not report illness either.
  • The UK analysis describes a borderline association for frequency of use (p = 0.09 in the model we checked) and a stronger one for showerhead cleaning (p = 0.05). We report these as the authors’ results, not as firm effects.
  • The EPA page does not give a figure for household shower risk. It gives an estimate for hospitalizations at the national level, which we did not use as a home risk figure.
  • We did not verify whether a shower filter, a shower head replacement, or a disinfection product reduces Legionella in a home. None of the three sources tests those steps.
  • The EPA page does not give a testing protocol for households, so this guide does not describe one.

How we chose

We chose the EPA page as the general reference because it is a federal source on drinking water and premise plumbing. We chose the two household studies because they test showers directly rather than large building systems. The UK study was checked as an abstract, and the Adelaide study was checked as full text. The quotes in this guide were checked against the saved source text. We did not use retail listings, product pages, or general blogs, and we have not named any product.

FAQ

Can a household shower make someone sick?

EPA says that people become exposed when they inhale water droplets containing the bacteria, and it says that most healthy people do not become infected after exposure. Higher-risk groups include people 50 years or older, smokers, people with chronic lung disease, and people with a weakened immune system.

How often should a shower be used?

The Adelaide authors identify showers used at least every week as associated with lower concentrations, and they recommend running showers every week to replace water in pipes. The sources do not give a number of minutes or a schedule beyond that.

Should I raise my water heater temperature to control Legionella?

The Adelaide authors name higher hot water temperature as a strategy, but the scald guidance names 120 degrees as a limit. Our sources do not resolve that conflict. Ask the local health department before changing the setting.

What if a household test is positive?

EPA advises consulting the state and county health departments and following the state, county, and city guidelines for the water supply.

Sources

Similar Posts