Legionella In Water (Everything You Need to Know in 2024)

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Legionella bacteria are found in surface water and groundwater supplies all around the world.

Legionella is a microorganism that, when inhaled in water droplets, causes a potentially fatal lung infection known as legionnaires’ disease.

In this guide, we’ve shared all the most important information about legionella in water, including what it is, how it gets there, and how to test for legionella bacteria.

📌 Key Takeaways:

  • Legionella is a bacterium that causes a type of pneumonia called legionnaires’ disease.
  • Legionnaires’ disease isn’t usually caused by drinking water containing legionella, but by inhaling airborne water droplets contaminated with the bacteria.
  • Since legionella is a microscopic contaminant, the only way to detect the bacteria in your water is with a laboratory water test.

❔ What Is Legionella In Water?

Legionella is a gram-negative bacterium that causes legionnaires’ disease, a lung infection that can be fatal. There are numerous species of legionella bacteria, and legionella pneumophila is the most likely to cause legionnaires’ disease.

Any water source can contain legionella, but still or stagnant, warm water sources are most likely to be contaminated with these bacteria.

Legionella is a hardy microorganism that can survive in a wide range of conditions and temperatures.

The EPA estimates that between 8,000 and 18,000 people are hospitalized every year with legionnaire’s disease.

You can’t usually get legionnaires’ disease from other people or from swimming in lakes, rivers, and ponds.

Legionella in tap water

🚰 How Does Legionella Get Into Water?

Unlike many other bacteria or microorganisms, legionella bacteria doesn’t come from another source (such as feces from an infected animal, for instance). It’s also not spread by person-to-person contact.

Instead, legionella grows readily in any suitable environment and is found in soils and fresh water sources around the world. The bacteria grow best at a temperature range of 77°F-113°F.

Some of the most common breeding grounds for legionella are man-made water systems, like water fountains, hot/cold water systems, cooling towers, building plumbing systems, hot tubs, and air conditioning units.

The presence of other germs in drinking water distribution systems, like nontuberculous mycobacteria and pseudomonas, is also more likely if legionella is detected.

🔎 How To Know If Your Water Contains Legionella

Legionella is a microscopic pathogen, so you won’t see this bacterium in your water supply. It also doesn’t have a taste.

Legionella is often present in stagnant water, which may have a musty smell. However, you shouldn’t rely on water smell alone to detect legionella, since often these bacteria are present in water with no unusual smell or taste.

Because of the difficulty in detecting legionella by sight, smell, or taste alone, we recommend using a more accurate means of detecting this bacteria.

If you get your water from a municipal supplier, you shouldn’t have to worry about testing for legionella because your local water utility should conduct regular legionella tests and take immediate action if such bacteria is detected.

However, if you have a private water supply or you have any other reason to be concerned about this bacteria, using a laboratory test is the best way to detect it in your water.

We’ve discussed testing for legionella bacteria later in this article.

Legionella in petri dish

🚱 Is Legionella In Drinking Water Dangerous?

Low levels of legionella bacteria in a potable water supply aren’t usually considered harmful. And drinking legionella usually isn’t dangerous because these bacteria only affect the lungs and aren’t harmful when ingested.

However, you can still get sick from drinking legionella in your water if some of the water accidentally enters your lungs.

And if your home’s water supply contains legionella, there’s a potential for you to catch legionnaires’ disease from breathing in airborne water droplets while you shower, run a faucet, or use any other appliance that releases water vapor into the air.

For this reason, although it’s not usually considered dangerous to drink water contaminated by legionella bacteria, having legionella-contaminated water in your home is still dangerous and should be addressed as quickly as possible.

The symptoms of legionnaire’s disease include:

  • Cough
  • High temperature & fever
  • Muscle aches
  • Headache
  • Other flu-like symptoms.

If left to advance, legionnaires’ disease may cause pneumonia, or inflammation of the lungs, which can be fatal.

People who are most likely to get seriously ill from legionnaires’ disease are people aged 50 or older, people with a chronic lung disease (like chronic obstructive pulmonary disease), former smokers, and people with a weakened immune system.

Diarrhea, vomiting, and mental confusion are other, less common symptoms of this disease. You may need antibiotics, and you’ll need to be hospitalized if you have severe pneumonia or complications caused by a weakened immune system.

📉 Is Legionella In Tap Water Regulated?

Yes, legionella is regulated in tap water in the US by the Environmental Protection Agency (EPA).

The EPA has established a Surface Water Treatment Rule that all regulated public water systems must adhere to. This rule requires water utilities to filter and disinfect public drinking water supplies to make them safe to drink and free from microorganisms.

There currently isn’t an EPA MCL (Maximum Contaminant Level) for legionella bacteria in drinking water, which means that, while public water systems must prove that they’re doing what they can to control legionella, there is no maximum amount of this bacteria that should be present in the water.

Public water systems are monitored by public health officials, who analyze the water system safety and assess their water treatment procedures.

Under EPA rules, public water systems must act accordingly if legionella bacteria is detected in a drinking water supply. This means taking extra steps to kill or remove the legionella as soon as possible, usually by temporarily increasing the water’s chlorine content.

Water utilities should inform their customers if legionella is detected in their water supply, offer advice and precautions while the issue is being treated, and outline how the problem will be resolved.

Testing water quality

🧪 How To Test For Legionella In Tap Water

There are a few different ways that you can test for legionella in a water supply in your home:

DIY Test Kits

A few brands sell DIY legionella test kits that give you test results on-site within a few minutes.

You can’t test for legionella with a simple test strip and color chart kit, so you will need to look for something slightly more advanced.

A new rapid method of testing for legionella in water is to use a lateral flow test (those that are used for COVID and pregnancy testing) that detect the Legionella pneumophila sg1 antigen – which causes the majority of legionnaires’ disease cases (around 90%).

You can also use thermometry testing devices that can be used to test for water temperatures in which legionella bacteria are likely to grow.

Laboratory Tests

Laboratory testing is the most commonly available testing type for legionella.

Water testing with tap score

Lab tests cost around $200-$300 and provide a detailed, quantified analysis of the legionella concentrations detected in your water. The best laboratory tests can detect a variety of Legionella species, including legionella pneumophila, legionella bozemanii, legionella dumoffii, legionella gormanii, and more.

To test for legionella with a laboratory test, follow these steps:

  1. Choose a legionella test from a trusted, certified water testing laboratory.
  2. Wait for the test to arrive in the post, then use the included equipment to take a sample of your water.
  3. Send your water sample to the laboratory and wait the specified time (usually 10-14 days) for the test results to be returned via email or post.
  4. Read through your results to learn of your water’s legionella bacteria content.

Since laboratory testing is so expensive, we only recommend this method if you have a reason to be concerned about this bacteria in your water supply. For instance, if someone in your home has contracted legionnaires’ disease, you should test all possible water outlets in your home (including stagnant water fixtures, infrequently used outlets, and air conditioning units).

Tap score water testing

👩🏽‍⚕️ What To Do If You’re Concerned About Legionella In Your Water

If you’re concerned about legionella in your water, or you think you have contacted legionnaires’ disease, there are a few different things you can do:

  • Arrange an appointment with your doctor, who can confirm whether or not you have legionnaires’ disease.
  • Consider hiring a water hygiene consultant to assess your home and identify the possible causes of legionnaires’ disease. A specialist can also rule out the possibility of legionella growth in your home, which tells you that you’ve contracted the disease from elsewhere.
  • Take the appropriate steps to reduce the likelihood of legionella growth in your home’s water fixtures and appliances. Remove any dead legs or dead ends in your pipework and flush out infrequently used faucets, showers, and other fixtures at least once a week. Make sure your air conditioning units, hot tubs, pools, and humidifiers are properly maintained.
  • Consider outside sources of legionella exposure. Legionella contamination in public places, like hospitals, gyms, hotels, car air conditioning units, and offices, is more likely than contamination of residential plumbing systems.

📑 Final Word: Removing Legionella From Water

If legionella is detected in any water source in your home, you should take steps to remove this bacteria from your water as soon as possible.

Legionella bacteria in your water supply should be treated with chemical shock – where your water utility temporarily uses elevated levels of a disinfectant (usually chlorine) to kill the bacteria.

You can prevent legionella growth in your pipes and plumbing system by installing a water filter system that’s capable of killing or removing this bacteria. It doesn’t particularly matter where the filter is installed, as long as it’ll remove the legionella from your water before it leaves the fixture (i.e. your shower or faucet), so that it isn’t present in your water vapor.

RKIN U1 countertop RO dispensing cool water

A standard water filter can’t remove legionella since the bacteria are small enough to pass through a filter’s pores. There are a few different advanced treatment types that can be used to remove legionella:

Remember, legionella is a deadly bacterium, so make sure to employ an effective treatment method and test your water after doing so to be certain that the solution is working.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

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