How does continuous dosing work in a water system?

When a water system has recurring microbiological problems, a one-off treatment is not always enough.

A system can first be sanitised and produce good water samples, but if the same conditions remain, bacteria and biofilm can start to build up again.

Continuous dosing is therefore used in some systems to maintain a stable level of disinfection over time.

The principle is that a controlled amount of disinfectant is continuously added in relation to water flow, water volume or other control parameters.

The goal is not to continuously overdose the system.

The goal is to maintain a consistent and controlled treatment level.

Short answer, what is continuous dosing?

Continuous dosing means that disinfectant is added automatically or regularly to a water system to maintain microbiological control.

It is used, among other things, in systems where:

• Water is continuously refilled
• Bacteria are at risk of recurring
• Biofilm is part of the problem
• The system is large or complex
• Water quality needs to be stable over time

The aim is to avoid repeated manual one-off treatments

What is the difference between one-off treatment and continuous dosing?

The difference is primarily about purpose.

One-off treatment

Used to treat an existing problem or sanitise a system.

Continuous dosing

Used to keep the system stable after control has been achieved.

It is therefore common to think in two steps:

Step 1: Sanitize the system

Step 2: Maintain control

The two steps may require different concentrations, contact times and strategies.

Why might continuous treatment be necessary?

A water system is dynamic.

New water comes in.

Water is used.

The temperature changes.

New microorganisms can be introduced.

The system contains many surfaces where biofilm can establish itself.

This means that a system that is clean today does not automatically remain microbiologically stable over time.

Continuous dosing can therefore be used to reduce the risk of microbiological load building up again.

How is the disinfectant dosed?

There are several technical solutions.

Dosing can, for example, be controlled based on:

• Water flow
• Water volume
• Time interval
• Concentration in the system
• Sensors or measured values
• System usage patterns

In a simple system, dosing can be relatively straightforward.

In a larger system, control may need to be adapted to varying flows and loads.

What is flow-controlled dosing?

Flow-controlled dosing means that the amount of disinfectant is adjusted according to how much water passes through.

If the flow increases, so does the dosing.

If the flow decreases, the dosing decreases.

This allows the treatment level to be kept more even even when water consumption varies.

This is particularly relevant in systems where the load changes during the day.

Why is correct dosing important?

Too low dosing can lead to insufficient microbiological control.

Too high dosing can be unnecessary and in some systems create other problems.

Therefore, dosing should be based on:

• Water quality
• Microbiological load
• System size
• Flow
• Contact time
• Materials in the system
• Chosen disinfection method

The goal is controlled treatment, not maximum concentration.

Do you need to measure the concentration in the system?

In many technical systems, follow-up is important.

This may involve checking:

• Disinfection level
• Flow
• pH
• Temperature
• Microbiological samples
• Other process parameters

Which measurements are needed depends on the system's requirements and treatment method.

Continuous dosing works best when combined with follow-up.

How does water quality affect dosing?

Water quality affects how much disinfectant actually remains available for microbiological control.

Water with a high load of, for example:

• Organic matter
• Sediment
• Iron
• Manganese
• Other reactive substances

can consume more of the treatment.

This means that the same dosing does not automatically work in all systems.

What is the demand for disinfectant?

The term describes how much of a disinfectant is consumed through reactions in the water and system.

If much of the treatment reacts with other substances, less may remain for microbiological control.

A heavily loaded system may therefore need a different treatment strategy than an already clean system.

What happens with biofilm?

Continuous dosing can be relevant for keeping biofilm under control over time.

But a heavily established biofilm may first require initial sanitisation.

It is important to understand the difference.

Continuous low dosing is not always the best method for quickly removing an old and severe biofilm problem.

A common approach is therefore:

Sanitize first

Then stabilize

Read more in our article: What is biofilm and why is it a problem in water systems?

Can continuous dosing prevent bacteria from returning?

It can reduce the risk.

But continuous dosing does not solve all system problems.

If there are:

• Blind pipes
• Stagnant water
• Poor circulation
• Contaminated filters
• Incorrect temperatures
• Poor maintenance

bacteria can still find favourable conditions locally.

That's why continuous treatment should always be seen as part of a larger hygiene effort.

What is a residual level?

Residual level is the amount of active disinfectant remaining in the water after some has been consumed in the system.

A remaining residual level can in some systems be important to protect the water further out in the distribution network.

How the residual level should be measured and what level is relevant depends on the treatment method and application.

Why does contact time still matter?

Even with continuous dosing, the disinfectant needs time to act.

The effect is influenced by:

• Concentration
• Contact time
• Temperature
• Water quality
• Microbiological load
• A system with a very short retention time may therefore need to be analysed differently than a system with a longer contact time.

What does retention time mean?

Retention time is the time water spends in a certain part of the system.

It is affected by:

• Tank volume
• Pipe length
• Flow
• Consumption
• Circulation

Retention time is important because it affects both disinfection and the risk of stagnant water.

Can you dose directly into a tank?

Yes, in some systems.

But how dosing should be done depends on the tank's function and how the water circulates.

If the treatment is added to a tank, it must be ensured that it is distributed evenly enough.

Poor mixing can otherwise lead to different concentrations in different parts of the system.

Can you dose directly into a pipeline?

Yes.

In-line dosing is used in many technical systems.

The treatment is then added to the water passing through the pipeline.

This can provide good control when dosing is linked to flow.

But even here, you need to understand what happens further out in the system.

Where should you measure?

There is no general answer.

Measurement points may be needed at:

• Dosing inlet
• After contact tank
• In the distribution network
• At critical draw-off points
• In the return line
• At the system's outermost points

The goal is to understand how the treatment actually works throughout the installation.

What happens if water consumption varies greatly?

This is one of the reasons why automated dosing can be valuable.

For example, in:

• Hotels
• Hospitals
• Industries
• Pools
• Spas
• Properties

water usage can vary greatly throughout the day.

Fixed dosing without connection to actual flow can then result in uneven treatment.

What happens if the system stops?

Stagnant water is a particular challenge.

When the flow stops, the following can occur:

• Temperature changes
• Disinfection level decreases
• Contact time increases
• Biofilm affects the system
• Water quality changes
• It is therefore important that the system's control also takes into account periods of low or no consumption.

Is continuous dosing the same as always having a lot of chemicals in the water?

No.

On the contrary, well-functioning continuous dosing is about control.

The goal is to use the right amount for the current system.

Automated control can make it possible to adapt dosing to actual needs instead of manually adding large quantities on single occasions.

What is the role of chlorine dioxide?

Chlorine dioxide is used in some water systems for continuous microbiological control.

One reason is that the substance has different chemical properties than traditional chlorination.

This can be relevant in systems where:

• Biofilm is a risk
• pH varies
• Microbiological control needs to be maintained throughout the distribution system

Read more in our article: Chlorine dioxide or chlorine, what is the difference?

Continuous dosing and Legionella

Legionella is an example of a problem where repeated acute sanitisation alone is not always the best long-term strategy.

If the basic conditions in the system still favour the bacteria, the problem may recur.

A long-term strategy therefore needs to combine:

• Temperature control
• Good circulation
• Minimisation of stagnant water
• Biofilm control
• Sampling

If necessary, continuous microbiological treatment

Read more in: What is Legionella and how does the bacteria arise in water systems?

Can continuous dosing be used in properties?

Yes, depending on the system and needs.

It can be relevant in, for example:

• Potable water systems
• Technical water systems
• Circulation systems
• Properties with recurring microbiological problems

The choice always needs to be adapted to the use and applicable requirements.

Can it be used in industry?

Yes.

Industry has many types of water systems where microbiological growth can affect:

• Process quality
• Operation
• Energy consumption
• Filters
• Heat exchangers
• Piping systems
• Maintenance

In such systems, continuous microbiological control can be part of process operation.

Can it be used in pools and spas?

Pools and spas require continuous control of water quality because people regularly introduce microbiological and organic loads.

The treatment strategy needs to be adapted to:

• Pool volume
• Bather load
• Circulation
• Filtration
• Temperature
• Water chemistry

Continuous dosing is therefore an established principle in many types of pool systems.

Can it be used in hospitals?

Hospitals and other healthcare environments may have particularly high demands on microbiological control.

Water systems can also be large and complex.

If continuous treatment is required, the system therefore needs to be dimensioned, monitored and documented based on the specific installation.

What happens if the dosing system stops?

This is an important practical question.

An automated system needs to be able to handle:

• Empty chemical container
• Pump failure
• Power outage
• Sensor failure
• Communication failure
• Deviating flow
• Therefore, modern systems can include:
• Alarms
• Level monitoring
• Flow control
• Remote monitoring
• Automatic shutdown

Exact function depends on the system's requirements.

Does dosing equipment need maintenance?

Yes.

Just like other technical equipment, it needs to be:

• Checked
• Calibrated
• Serviced
• Be cleaned
• Consumable parts replaced
• Chemical levels monitored

A dosing system is not "install and forget."

How do you know if continuous dosing is working?

The effect should be monitored.

This can be done, for example, by:

• Measuring treatment level
• Microbiological water samples
• Sampling at multiple locations
• Biofilm control
• Trend analysis
• Operating data
• Temperature and flow measurement

It is important not to look solely at a single number.

The system's long-term development is more valuable.

How does Xinix work with continuous dosing?

FreeBact® Dosage is Xinix's product line for smart continuous dosing in water systems.

The systems are developed for various types of applications, from properties and industries to pools, spas, and hospitals.

The principle is that FreeBact® is dosed in a controlled manner based on the system's needs.

For a system with existing microbiological problems, one first needs to assess:

• Water quality
• System design
• Biofilm
• Flows
• Water volume
• Current treatment
• Microbiological results

Thereafter, an appropriate treatment strategy and dosing solution can be developed.

Common questions about continuous dosing

Do all water systems need continuous dosing?

No.

It is relevant where there is a need for ongoing microbiological control.

Is continuous dosing better than one-time sanitation?

They have different purposes.

Sanitation treats an existing problem. Continuous dosing is used to maintain control.

Can continuous dosing remove old biofilm?

A heavily established biofilm may first require a specific sanitation.

Continuous treatment is then used to keep the system stable.

Is the same amount dosed all the time?

Not necessarily.

A modern system can adjust the dosing based on, for example, water flow.

Can the dosage be too high?

Yes, if the system is incorrectly configured.

That is why control, measurement, and follow-up are important.

Do you still need to take water samples?

Yes.

Continuous dosing does not replace the need for follow-up.

Does continuous dosing help against Legionella?

Continuous microbiological treatment can be part of a Legionella strategy, but temperature, circulation, biofilm, and system design also need to be managed.

Can dosing be remotely monitored?

It depends on the equipment.

Modern dosing systems can be built with different levels of monitoring, alarms, and communication.

Summary

Continuous dosing means that a controlled amount of disinfectant is continuously added to a water system.

The purpose is to:

• Maintain microbiological control
• Reduce the risk of regrowth
• Control biofilm over time
• Adapt treatment to water flow and needs
• Create more stable water quality

But the technology works best as part of a holistic strategy.

Good circulation, correct temperature, clean systems, functioning filters, and follow-up are still important.

The central principle is therefore:

Sanitize the problem, address the cause, and then keep the system stable.

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Contact

Thank you for reading this far!
If you have any questions or concerns, please feel free to contact us.

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