Disinfectant Depletion and Regrowth in Waterlines: What the 2026 Dental Study Shows
An evidence-led guide for understanding biofilm in managed water and hygiene systems.
Narrow-bore polymer waterlines consume chlorine dioxide within hours, and a 2026 dental waterline study shows how that depletion turns a one-off shock into a transient result while a sustained low-level presence held counts down.
The 2026 dental waterline study
A clinical hygiene study published in PLOS ONE on 5 March 2026 (Winkler et al., University Hospital Münster, doi 10.1371/journal.pone.0342347) compared automated chlorine dioxide flushing protocols in a dental chair unit, a system of several metres of small-diameter polymer tubing fed with tap water. Microbial load was measured by flow cytometry (intact and total cell counts) alongside agar culture, so the results include cells that culture methods miss.
After stagnation the tubing water reached intact cell counts of around a million cells per millilitre. A single shock at about 22.7 mg/L chlorine dioxide reduced intact cell counts by up to roughly 2.5 log₁₀, but counts recovered to near their starting level within about 72 hours of resuming ordinary use and stagnation. A one-day low-dose flushing routine also produced only a temporary reduction. By contrast, continuous application of 1.2 mg/L chlorine dioxide over several days achieved a reduction of up to 2.51 log₁₀ that was maintained while dosing continued; doubling the concentration to 2.4 mg/L gave no meaningful further benefit.
The authors also documented depletion: the measured chlorine dioxide concentration inside the unit fell over a few hours regardless of the microbial load, which they attributed to reaction with organic and inorganic material in the water and with the large surface area of polymer tubing. That depletion is the mechanism behind the recovery seen after shock treatment.
Why shock and sustained dosing behave differently
A shock delivers a large, brief oxidant demand. Where it reaches attached growth it can detach and inactivate material, and the study demonstrated visible biofilm removal on experimentally grown Pseudomonas aeruginosa biofilm. But once the concentrated solution is flushed out or consumed, any surviving cells, cells re-introduced with fresh tap water, and material in poorly flushed sections can recolonise the surfaces. The reduction is real but transient.
Sustained low-level dosing keeps an active concentration present during the stagnation periods in which regrowth would otherwise occur. In the study this was the difference between a reduction that lasted days and one that lasted hours. The authors' recommendation for waterlines of this kind was continuous low-dose application, with periodic shock reserved for units that are already heavily contaminated after long standstill.
What this study does and does not establish
It establishes, for one dental chair unit under controlled conditions, that continuous low-dose chlorine dioxide sustained a microbial reduction that single shocks did not, and that chlorine dioxide depletes quickly in polymer-tubed systems. It is consistent with the general principle that biofilm control in narrow, intermittently used waterlines depends on keeping a disinfectant present rather than applying it occasionally.
It does not establish a dose for any other system. The authors state plainly that only one unit was examined, real patient use was simulated rather than performed, the biofilm test was simplified, no long-term trial was run and long-term material compatibility at higher concentrations remains to be studied. The chlorine dioxide was generated on site by the researchers' own dosing equipment; ChloroKlean products were not tested. The findings therefore inform how to think about residual versus shock in waterlines; they do not verify any product, label claim or authorisation.
Evidence and uncertainty
Published biofilm studies are valuable for understanding mechanisms, but their conditions may not match a particular installation. Species, surfaces, deposits and operating conditions should be recorded when interpreting evidence.
For safety-critical systems, decisions should be documented through the relevant risk assessment and management plan.
Choosing the next question
A useful next step is to identify what is known, what is inferred and what needs verification. This avoids treating a general reference as a site diagnosis.
Where a product is considered, confirm the intended use, authorisation and label directions independently of this educational guide.
A proportionate biofilm-management approach
Use this sequence to frame investigation and control; it is not a dosing protocol.
Define the system and risk
Map wetted surfaces, operating conditions, users and relevant legal or sector guidance.
Gather evidence
Review inspection, operational, residual and microbiological records rather than relying on one indicator.
Address contributing conditions
Consider cleaning, hydraulics, nutrients, stagnation and equipment condition alongside any authorised biocide programme.
Verify and review
Document the intervention and review results through the site’s written scheme or hygiene plan.
Expert Insights
"Biofilm control is a system-management question: chemistry, surfaces, flow, cleaning and verification all matter."
ChloroKlean Technical Team
Technical review team
About the Reviewer
Gavin Owen
Managing Director, ChloroKlean
Gavin Owen leads ChloroKlean's technical and commercial operations, bringing over 20 years of experience in industrial chemical distribution and water treatment. He oversees product development, regulatory compliance strategy, and the company's BPR compliance programme across PT2, PT4, PT5, and PT11 product types. Gavin works directly with water treatment professionals, facilities managers, and public health engineers across healthcare, leisure, food processing, and industrial sectors.
Frequently Asked Questions
Common questions about this topic, answered by our technical team.
Scope and safe-use note
- This is general educational information, not a dosing instruction or a product label.
- Use only a biocidal product authorised for its intended product type and follow its label, Safety Data Sheet and site risk assessment.
- Investigate system design, cleaning, monitoring and microbiological findings with a competent person where there is a health risk.
Published evidence about a disinfectant or another product does not establish efficacy, authorisation or an appropriate use pattern for any ChloroKlean product.
Related Resources
Continue exploring our knowledge base and product information.
Biofilm learning hub
Browse the connected biofilm guides.
Disinfectant residuals and biofilm control
What a residual can and cannot tell you.
Chlorine dioxide and biofilm: the evidence
How to read chlorine dioxide biofilm studies.
Continuous vs shock treatment
ChloroKlean's application page on dosing approaches; this guide interprets the published evidence only.
PT5 drinking-water products
Product-type information for potable-water applications.
Sources & References
This article references guidance from the following authoritative sources:
- Biofilms: survival mechanisms of clinically relevant microorganisms
Industry Standard - Frontiers in Microbiology (PMC)
- Legionella and the prevention of legionellosis
WHO - World Health Organization
- ACOP L8: Legionnaires' disease
HSE - Health and Safety Executive
- Biocidal Products Regulation
ECHA - European Chemicals Agency
- Chlorine dioxide flushing protocols for microbial reduction in dental chair units (5 March 2026)
Industry Standard - PLOS ONE
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