Legionella in Motorhomes: Identify Bacteria and Test Drinking Water

Whether you are staying at a campsite, travelling on a road trip or spending an extended period at a motorhome stopover, fresh water is an essential part of everyday life. It is used for washing hands, cooking, brushing teeth and often showering. But how hygienic is the water when it has been sitting in the fresh water tank for several days?

Legionella and other bacteria can occur in water systems under unfavourable conditions. Long periods of stagnation, biofilms in pipes, unsuitable water temperatures and inadequate cleaning are particularly relevant. Contaminated water does not necessarily have an unusual smell or appear visibly dirty.

At Umweltcheck, we regularly receive enquiries from customers concerned about water quality in motorhomes and campervans. We have also encountered elevated bacterial counts in water analyses. In this guide, we combine our practical experience from customer enquiries with essential information about water hygiene and explain when laboratory testing may be advisable.

1. How safe is drinking water in a motorhome?
2. Bacteria and Legionella in the fresh water system
3. Testing drinking water for bacteria and Legionella
4. Cleaning the water tank and preventing bacterial growth
5. FAQ: Legionella and drinking water in motorhomes

1. How safe is drinking water in a motorhome?

Water quality depends on more than the public water supply. What happens after the water enters the motorhome's water system is equally important. The fresh water tank, hoses, pipes, taps, pump and water heater form an interconnected system. Deposits can develop and microorganisms may multiply in different parts of this system.

If a motorhome is used only occasionally, water may remain in the tank for extended periods. During warm weather, the water may also heat up. At the same time, certain sections of the pipework may rarely be flushed with fresh water. This combination can adversely affect water hygiene.

Why can water quality deteriorate?

• Long periods of stagnation: When water is not replaced for an extended period, existing microorganisms may multiply under suitable conditions.
• Elevated temperatures: A hot vehicle interior or an inadequately managed water heater can encourage the growth of certain microorganisms.
• Biofilm: Microbial deposits can develop on the internal surfaces of tanks, hoses and fittings.
• Contamination during filling: Dirty filling points, unsuitable hoses or unhygienic connections can introduce microorganisms into the system.
• Infrequent use: Rarely used showers and taps can lead to longer water retention times.

Can contaminated drinking water be recognised?

Some problems may become noticeable through unusual odours, discolouration, slime or visible deposits. These changes should be treated as warning signs. However, clear and odourless water is not necessarily free from bacteria or other contaminants.

Microbiological contamination generally cannot be assessed by sight alone. Anyone wishing to determine whether relevant microorganisms are present needs an appropriate water analysis.

From our experience: High bacterial counts in motorhome water

At Umweltcheck, we regularly receive enquiries from motorhome and campervan owners about the quality of their drinking water. Common concerns include prolonged periods of stagnation, fresh water tank hygiene and unexpected laboratory results.

An anonymised example from our practical experience, with slightly adjusted figures: One water analysis showed approximately 5,200 CFU/ml at 36 °C and 700 CFU/ml at 22 °C. These results indicate a high microbial load. However, no coliform bacteria were detected in the sample.

Possible contributing factors include prolonged water stagnation, elevated temperatures or biofilms inside tanks and pipes. The exact cause cannot be determined from bacterial counts alone. Comparisons with regulatory requirements also depend on the analytical method and testing conditions.

In this case, we advised the customer to thoroughly clean the entire water system, disinfect it using a product suitable for the drinking water installation and rinse it carefully afterwards. A follow-up bacteriological water analysis can help determine whether these measures have been successful.

Our experience shows: Even water that looks clear and has no unusual smell can contain a substantial bacterial load. Laboratory testing provides valuable information for assessing water hygiene and deciding whether further action is needed.

Which parts of the system require special attention?

The fresh water tank is only one part of the system. Taps, shower hoses, shower heads, filter housings and the hot water system may also be relevant to water hygiene. Areas where water remains stagnant require particular attention.

Cleaning only the tank while neglecting hoses, fittings and the water heater may not produce lasting improvements. The entire water system should therefore be considered.

2. Bacteria and Legionella in the fresh water system

Different microorganisms can occur in water. Not every detectable microorganism represents an immediate health risk. However, some bacteria are important indicators of drinking water hygiene. Others, particularly Legionella, are especially relevant because of their potential health effects.

What is Legionella?

Legionella bacteria can occur naturally in water. Under favourable conditions, they can multiply in engineered water systems. Such conditions include suitable temperatures, biofilms and prolonged water stagnation.

The main health concern is inhaling tiny water droplets containing Legionella. These fine aerosols can be generated when showering, for example. Drinking water containing Legionella is not the usual route of transmission for Legionnaires' disease.

For more information about health effects, symptoms and preventive measures, read our specialist article Dangerous Legionella in Water.

Which temperatures encourage Legionella growth?

Temperature is an important factor in Legionella growth. Lukewarm water can provide particularly favourable conditions. Cold water should therefore be kept as cool as possible, while hot water systems should be operated in accordance with manufacturer instructions and appropriate hygiene recommendations.

What role does the water heater play?

Many motorhomes have a hot water system or a combined heating and hot water unit. If water is heated only occasionally, different temperature zones may develop. Residual water may also remain in pipes and shower hoses.

Appropriate hot water hygiene therefore considers not only the selected heater temperature but also actual usage, periods of stagnation and the characteristics of the system. Not every installation is designed for permanently high temperatures or thermal disinfection procedures.

Which other bacteria are relevant in drinking water?

For more information about possible contamination and health risks, see our guide Bacteria in Drinking Water.

The significance of a laboratory result depends on the parameters tested, how the sample was collected and the intended use of the water. Individual measurements should therefore always be assessed in the context of sampling conditions and the state of the water system.

Biofilm: Why bacteria can return after cleaning

A biofilm is a community of microorganisms that can establish itself on surfaces. In a fresh water system, these deposits may develop on tank walls, inside hoses, on seals and in hard-to-reach areas.

Biofilms can protect microorganisms from external influences and make cleaning more difficult. Simply refilling the tank with fresh water or circulating a cleaning agent through the pipes may therefore be insufficient.

Heavily soiled tanks may require thorough manual cleaning. Accessible deposits should be removed before further cleaning or disinfection measures are carried out. It is essential that all products and procedures are suitable for the specific drinking water installation.

3. Testing motorhome drinking water for bacteria and Legionella

Anyone who wants to assess water quality beyond its appearance and smell can arrange a laboratory analysis. With our water testing kits, you can collect the sample yourself and send it for examination. The laboratory then tests the sample for the selected microbiological parameters.

When general bacterial contamination is suspected, different parameters may be relevant than when specifically testing for Legionella. Legionella testing can be particularly useful for motorhomes with showers because showering produces fine water droplets.

When is water testing advisable?

• After extended periods of non-use, when there is uncertainty about water hygiene.
• If unusual odours, visible deposits or recurring hygiene problems occur.
• After confirmed microbiological contamination, to check the effectiveness of appropriate corrective measures.
• When purchasing a second-hand motorhome with an unknown maintenance and cleaning history.
• When water is regularly used for drinking, cooking, brushing teeth or showering and additional reassurance is desired.

From our customer enquiries, we know that prolonged periods of non-use often raise questions about water quality. We help customers select a water analysis that matches their specific concerns and testing requirements.

Which water analysis is suitable for a motorhome?

At Umweltcheck, we offer both a separate Legionella analysis and combined water testing packages. If you only want to test for Legionella, the individual analysis is a suitable option. If several bacterial and water quality parameters need to be checked, a combined analysis may be more economical than ordering several individual tests. You collect the water sample yourself and return it to us.

How does the motorhome water test work?

With our water testing kits, you can collect a sample directly from your motorhome. After placing your order, you receive the necessary sampling materials and instructions. A visit from a specialist is not required.

1. Order a water test: Choose the appropriate analysis and order your testing kit from Umweltcheck.
2. Receive your testing kit: The package contains the required sampling containers and instructions for correct sampling and return shipment.
3. Collect the water sample yourself: Take the sample from the selected water outlet in your motorhome. Follow the supplied instructions to help ensure meaningful results.
4. Return the sample to Umweltcheck: Package the sample according to the instructions and send it back under the specified transport conditions.
5. Laboratory analysis and results: The sample is examined for the selected parameters in the laboratory. You then receive your test results.

Correct sampling is particularly important for microbiological examinations. Unsuitable containers, contamination during collection or failure to observe transport requirements can affect the result. Always follow the instructions supplied with the testing kit.

When testing for Legionella, the sampling location is also important. A sample taken directly from the tank does not necessarily answer the same question as a sample collected from the shower. The procedure followed before sampling can also influence the findings.

What does a laboratory result tell you?

A laboratory report describes the sample tested at the time of collection and within the scope of the analytical method used. It does not automatically establish the hygienic condition of every pipe and water outlet.

If abnormal values are detected, possible causes should be investigated and appropriate measures taken. Depending on the findings, repeat testing may be advisable. Water testing does not replace regular cleaning or proper operation of the fresh water system.

Elevated bacterial counts can raise questions about what the results mean in practice. Through our customer support experience, we are familiar with these concerns and help customers understand the scope and significance of their water analyses. Depending on the findings, a detailed hygiene assessment may require additional specialist advice.

4. Cleaning the water tank and preventing bacterial growth

Good drinking water hygiene begins before the tank is filled. Clean connections, suitable drinking water hoses and a regularly maintained water system help reduce avoidable contamination.

The necessary cleaning frequency depends on usage, periods of non-use, environmental conditions and manufacturer recommendations. A single fixed cleaning interval is therefore not appropriate for every vehicle.

Step by step towards a hygienic water system

1. Inspect the water system

   Check the tank, filling point, cap, seals, hoses and accessible connections for deposits, dirt and damage.

2. Drain old water

   Remove stagnant water from the system. Follow the vehicle manufacturer's instructions for draining the tank, water heater and pipework.

3. Carry out preliminary mechanical cleaning

   Where surfaces are accessible, suitable cleaning tools can help remove deposits. Removable tanks may be particularly easy to clean thoroughly.

4. Use an appropriate cleaning procedure

   Only use products specifically suitable for drinking water systems and the installed materials. Follow the manufacturer's instructions regarding dosage and contact time.

5. Include pipes and water outlets

   Taps, shower hoses and the hot water system also require attention. Observe the relevant technical instructions when cleaning them.

6. Rinse thoroughly and refill

   Remove cleaning product residues according to the instructions and refill the system with hygienically safe water.

Cleaning and disinfection: What is the difference?

Cleaning removes dirt, deposits and surface build-up. Disinfection, on the other hand, aims to reduce or inactivate microorganisms using an appropriate procedure.

These processes are not interchangeable. Disinfection may be less effective when biofilms or heavy deposits are present. Conversely, mechanical cleaning alone does not guarantee that all relevant microorganisms have been sufficiently reduced.

Is citric acid suitable for cleaning a water tank?

Citric acid is often discussed as a means of removing limescale. However, it is not equivalent to a validated disinfection procedure against Legionella. Material compatibility may also vary depending on the tank, seals, pump, water heater and fittings.

Citric acid and other household cleaning agents should therefore not be used without checking the manufacturer's instructions. Mixing chemicals yourself should be avoided.

How can water hygiene be improved in everyday use?

• Suitable water source: Whenever possible, use water from outlets clearly designated as drinking water sources.
• Hygienic filling: Protect the filling point and drinking water hose from contamination.
• Replace water regularly: Avoid unnecessarily long periods of stagnation.
• Maintain the water system: Clean and service the installation according to usage and manufacturer recommendations.
• Monitor temperatures: Avoid excessive warming of cold water wherever possible.
• Inspect after extended breaks: Check the condition and hygiene of the system before using it again.

What should you do after a long period of non-use?

If a motorhome remains unused for weeks or months, follow the vehicle and component manufacturers' recommendations for draining, cleaning and recommissioning the water system. Correct draining is especially important when freezing temperatures are possible, to prevent damage to pipes, pumps and water heaters.

Before your next trip, inspect the system visually. If unusual odours, deposits or other abnormalities are present, investigate them before returning to normal use.

5. FAQ: Legionella and drinking water in motorhomes

Further information

When assessing drinking water hygiene and potential health risks, information from the relevant Swiss authorities and the operating and maintenance instructions provided by vehicle and equipment manufacturers are particularly important.

• Swiss Federal Office of Public Health (FOPH) – Information on Legionella and legionellosis
• Swiss Federal Food Safety and Veterinary Office (FSVO) – Drinking water and food safety
• Swiss Federal Office for the Environment (FOEN) – Information about water

Note: This guide provides general information. It does not replace an individual hygiene assessment, medical advice or the technical instructions issued by equipment manufacturers.