How to clean and disinfect a water tank?

A water tank may look clean and yet contain microorganisms and biofilm on its surfaces.

It is therefore important to distinguish between three different things:

• Emptying the tank
• Cleaning the tank
• Disinfecting the tank and water system

Pouring out old water and refilling with new changes the water volume, but does not automatically remove microorganisms attached to the tank walls, in hoses, or inside the piping system.

If the goal is a hygienically well-functioning water tank, one must therefore consider the entire system.

Short answer, how to clean a water tank?

A basic treatment can be divided into the following steps:

1. Drain the system
Remove old water.

2. Inspect the tank
Check for sediment, discoloration, deposits, or visible biofilm.

3. Mechanically clean where possible
Remove loose material and deposits.

4. Disinfect tank and piping system
Use a method and product intended for the specific application.

5. Allow the treatment to have the correct contact time
Always follow the product's dosing and usage instructions.

6. Check the entire system
Don't forget hoses, pumps, valves, and taps.

What is the difference between cleaning and disinfection?

This is one of the most important distinctions to understand.

Cleaning

Cleaning involves removing, for example:

• Sediment
  
• Dirt
• Particles
• Deposits
• Organic material

Disinfection

Disinfection involves inactivating microorganisms.

A tank can therefore be visually clean without being microbiologically controlled.

Similarly, disinfection works less effectively if the tank is full of dirt, sediment, or other deposits.

Cleaning and disinfection therefore complement each other.

Why isn't it enough to just change the water?

When the tank is emptied, the water within it disappears.

However, microorganisms can be attached to the inside of the tank.

If biofilm has already formed, it can remain on:

• Tank walls
• Bottom
• Pipes
• Hoses
• Pumps
• Valves
• Fittings
• Taps

When the tank is refilled, the new water comes into contact with the same surfaces.

This is why a system can sometimes experience recurring problems even if the water is changed regularly.

What is biofilm in a water tank?

Biofilm is a layer of microorganisms that attach to a surface and build a protective structure around themselves.

It can be:

• Thin
• Difficult to see
• Slippery or slimy
• Discolored
• Patchily distributed

Biofilm does not necessarily look like a thick layer of dirt.

Even a tank that appears relatively clean can have microbiological growth on its surfaces.

Please read our article: What is biofilm and why is it a problem in water systems?

How does biofilm form in a tank?

Several factors can contribute.

Examples include:

• Stagnant water
• Heat
• Long periods between cleanings
• Poor water quality during filling
• Organic material
• Hard-to-reach surfaces
• Water that is regularly refilled without the tank being emptied
• Hoses and pipes that are not cleaned
• Biofilm is therefore often a system problem rather than a problem only found in the tank itself.

Should the tank be cleaned mechanically?

If the tank is accessible and has visible deposits, mechanical cleaning can be an important part of the process.

This may involve removing:

• Sediment
• Loose deposits
• Dirt
• Other material

The appropriate method depends on the tank's material and construction.

Tools or cleaning methods that can damage the surface should be avoided, as scratches and damage can create new areas where material and microorganisms can more easily accumulate.

Does a tank need to be cleaned if the water looks clean?

Yes, it may still need to be cleaned.

Clear water does not indicate the microbiological condition of the tank's surfaces.

Many microorganisms cannot be detected by:

• Sight
• Smell
• Taste

This means that a hygiene routine should not be based solely on how the water looks.

How often does a water tank need to be cleaned?

There is no single interval that suits all tanks.

The need is influenced by factors such as:

How often the tank is used

• Water source
• Temperature
• How long water stands stagnant
• Tank material
• System design
• Previous biofilm problems
• How well the tank is kept closed

A tank used daily under controlled conditions has different needs than a motorhome that stands unused all winter.

It is therefore better to have a well-thought-out routine based on usage rather than just following a general calendar interval.

What about motorhomes and caravans?

Water systems in motorhomes and caravans are particularly exposed to periods of stagnant water.

Common conditions include:

• Long periods of disuse
• High summer temperatures
• Filling from different water sources
• Hoses used at campsites
• Tanks that are difficult to inspect
• Small pipe systems with multiple angles and connections
• This means that the entire system should be included in the cleaning, not just the tank.

What about a boat?

Boats also often have water systems that are used irregularly.

Temperature variations and longer periods in port or winter storage can mean that water stands stagnant for a long time.

Here too, one needs to consider:

• Tank
• Pipes
• Hoses
• Pumps
• Water heaters
• Taps

A clean tank system therefore does not begin and end at the container itself.

What about emergency tanks?

Emergency tanks are often used the opposite way; they can remain filled for a longer period before the water is needed.

Here, hygiene during filling and storage is particularly important.

The tank should:

• Be intended for drinking water
• Be clean before filling
• Be kept properly closed
• Be stored in a protected, cool, and dark place
• Be checked regularly
• Have a plan for turnover and cleaning

It is also important to remember that any water treatment does not replace the need for a clean container.

Do the hoses need cleaning?

Yes.

Hoses are part of the water system.

They have a large internal surface area relative to the amount of water and can be difficult to inspect.

If the disinfectant solution only treats the tank but is never circulated or passed through the hoses, an important part of the system is left untreated.

The same applies to:

• Pipes
• Valves
• Pumps
• Taps
• Shower heads
• Other dispensing points

Don't forget the filling hose

A separate detail often overlooked is the hose used to fill the tank.

If it is left:

• Warm
• Damp
• Open
• On the ground
• With water remaining inside

it can itself become a source of contamination.

A clean tank can thus be contaminated even during filling.

The filling hose should therefore be handled as hygienically as other parts of the drinking water system.

What happens if there is sediment at the bottom?

Sediment can consist of several different materials.

It can be, for example:

• Mineral particles
• Sand
• Rust
• Organic material
• Other particles from the water source

Sediment can provide surfaces and material for microorganisms to associate with.

If larger quantities of sediment are present, it should therefore normally be removed before disinfection.

Can ordinary dish soap be used?

It depends on the tank, system, and intended use.

For drinking water systems, it is important that products used do not leave unwanted residues or affect water quality.

The cleaning agent should therefore be suitable for the surface and use in question.

After cleaning, the system needs to be handled according to the product's instructions before it is reused for drinking water.

Can chlorine be used to clean a tank?

Chlorine-based products are used for disinfection in many types of water systems.

The effect depends on, among other things:

• Concentration
• Contact time
• pH
• Water quality
• Organic material
• Biofilm
• Materials in the system

It is important to use a product intended for the purpose and to follow the correct dosage.

More chemical does not automatically mean better results.

Can chlorine dioxide be used for a water tank?

Chlorine dioxide is used for disinfecting water and water systems.

It has different chemical properties than traditional chlorination and can be relevant where biofilm also needs to be managed.

The concentration and treatment needed depend on whether the goal is:

• Disinfection of drinking water
• Sanitation of the tank
• Treatment of the entire piping system

These are important distinctions.

Read more in: Chlorine dioxide or chlorine, what's the difference?

What is contact time?

Contact time is the time the disinfectant needs to be in contact with the water and the surfaces to be treated.

Therefore, it is not always enough to add a disinfectant and then immediately drain the system.

The effect depends on the combination of:

• Concentration
• Contact time
• Temperature
• Water quality
• Microbiological load

Always follow the instructions for the product and treatment used.

Should the treatment solution be run through the taps?

If the purpose is to disinfect the entire water system, the treatment must also reach pipes, hoses, and taps.

Otherwise, only the tank is treated.

A system can then still contain biofilm or microorganisms in the lines.

How this should be done depends on the system's construction and the treatment product used.

What to do after prolonged winter storage?

A system that has been unused for a long time should not automatically be considered hygienic just because it was drained before storage.

Moisture may remain.

Microorganisms may be present on surfaces.

A good start to the season can therefore be:

• Inspect the system
• Check hoses and fittings
• Clean the tank if necessary
• Disinfect the entire system
• Refill with good quality water
• Check odor, taste, and function
• What to do if the water smells bad?

An unusual odor may indicate that something has changed in the water or system.

Possible causes include:

• Microbiological growth
• Biofilm
• Materials in hoses or tank
• Long storage
• Organic material
• Chemical influence

One should then not just mask the odor or add more water.

The system needs to be assessed first and, if necessary, cleaned and disinfected.

Can cleaning be done without being able to open the tank?

Yes, many tank systems have limited physical access.

In such cases, system treatment becomes particularly important as mechanical cleaning of all surfaces is not possible.

The treatment then needs to circulate or otherwise come into contact with as much of the system as possible.

For heavily soiled tanks, physical cleaning may still be necessary where practical.

How does Xinix work with water tanks?

FreeBact® Water includes solutions for disinfecting drinking water, from smaller volumes to larger tanks.

For tank systems, it is important to distinguish between two different situations.

Ongoing treatment of drinking water

Here, the goal is to treat the water volume itself.

Sanitation of an existing system

Here, the surfaces of the tank and piping system also need to be included in the treatment, especially if biofilm is suspected.

For larger and continuous water systems, there is FreeBact® Dosage.

The right solution depends on the system's size, usage, and microbiological status.

Frequently Asked Questions about water tank cleaning

Is rinsing the tank with water enough?

Rinsing can remove loose material, but it does not necessarily remove biofilm or inactivate microorganisms.

Do I have to empty the tank before cleaning?

For a more thorough cleaning or sanitization, old water normally needs to be removed so that the system can be inspected and treated properly.

Can biofilm exist in a plastic tank?

Yes.

Biofilm can form on many types of water-contacting materials.

Can biofilm exist in a stainless steel tank?

Yes.

Stainless steel can be a good material for water systems, but no water-contacting surface is automatically free from microbial growth.

Do new tanks need to be cleaned?

It is wise to clean and check a new tank before it is put into service for drinking water.

Can I just refill with new water after winter?

It is better to first check the system's hygiene after a longer period of disuse.

Should taps and showers also be disinfected?

If they are part of the same water system, they should also be considered during system disinfection.

How do I know the tank is clean?

Visual inspection can provide some information but does not tell the whole story about microbiological status. In case of specific requirements, microbiological sampling may be needed.

Summary

Cleaning a water tank is about more than just changing the water.

Consider the entire chain:

• Empty old water
• Remove sediment and visible deposits
• Clean the tank
• Disinfect if necessary
• Also treat pipes and hoses
• Check the filling equipment
• Fill with good quality water
• Store stored water protected, cool, and dark

And most importantly:

A clean tank is not enough if the rest of the water system still contains biofilm.

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Contact

Thank you for staying with us all the way!
For questions & concerns, please feel free to contact us.

Alexandra Németh, Marketing Manager, Xinix Global AB
alexandra@xinix.se
Mobile: 070-78 601 678