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Dental unit waterlines are all the rage these days. On the surface, it can seem easy to tell the treatment options apart. Application, cost, and longevity are all important factors when selecting a waterline treatment solution. However, first, you want to know if the product you're spending money on actually works and will keep your dental lines safe.

After all, getting dental unit waterlines clean so you can deliver safe water into your patients' mouths and protect yourself (dentist) and your staff (dental nurses), is why you're working on waterline maintenance protocol in the first place!


In 2017, a company in USA conducted the most extensive dental waterline treatment efficacy study to date. Compiling data from over 22,000 consecutive waterline tests, this study shows vital real-world statistics of product performance in the marketplace.

Of these 22,000+ consecutive waterline tests, all samples were taken directly from clinical practices and provided by those practices. Treatment information was provided by dental practices as well.

Every sample was tested using the R2A heterotrophic plate count method. All tests were blind and utilised approved standard methods to ensure accuracy. All pass/fails were measured against the US standard for safe water of ≤500 CFU/ml, which is much more forgiving than UK standard for drinking water quality ≤200 CFU/ml

HTM01-05 TVC Sampling

HTM01-05 - Paragraph 6.79

"Where monitoring is undertaken, the TVC should be expected to lie in the range 100 to 200 colony forming units per millilitre (cfu/ml). In general, incubation should be at 22°C. These measurements can be carried out by commercial microbiological services or by Public Health England."

So, what are the key findings from the study?

Overall, 31% of treated waterlines failed to meet the US Standard of ≤500 CFU/mL, which means they have also failed the UK standard too.

However, tablets with an accompanied shock product showed the best results. A handful of product combinations were above 90% pass rate; however, these did not have extensive data sets.

Straws and cartridges passed at 72% on average.

Shock treatments used by themselves – with no accompanied continuous or daily treatment products – performed similarly well to everyday liquids and centralised systems at 60% or below.

So, how can treated waterlines fail this often?

This is for a few reasons. However, first, let's be clear: most of the products used in dental practices across the world are great products. Each of the treatment types and specific products have features and benefits that can be appreciated. But often, how products are sold is different than how they work in the real world.

These are the most common reasons we've found for poor performance:

1. Sold with Unrealistic Expectations

Products are often sold as maintenance-free, and unfortunately, none of them are.

A quick review of the instruction manuals shows that each product requires close attention and a little elbow grease to be effective. Whether that involves testing your water hardness, daily water bottle drying, water bottle washing, or performing a protocol multiple times to start, make sure you review the instructions for- use on a manufacturer's (not just supplier’s) website to know what a product requires.

2. Misunderstanding the science of low-level antimicrobials vs biofilm

There are two kinds of dental waterline treatment products: continuous treatments (low-level antimicrobials) and shock treatments (high-level disinfectants).

Continuous treatments contain low-level antimicrobials that maintain already clean lines while also being safe for patient contact. They continuously fight bacteria within the lines.

Shock treatments contain high-level disinfectants that are strong enough to remove biofilm. They effectively remove (or "shock the system") bacteria and biofilm but are not safe for patient contact.

Shock treatments clean the waterlines. Continuous products maintain the already clean lines for longer before another shock treatment is required. When used together, pass rates go way up. When used separately, results are wildly inconsistent.

The shock treatment should be repeated regularly:

Shock Every 1-3 Months - The best products recommend shocking your dental unit waterlines between 1-3 months. Effective resistance against microbial growth slowly diminishes within this timeframe and biofilm counts can quickly rise towards the maximum 200 CFU/mL limit. During the disinfection, planktonic organisms will be destroyed, but even if the majority of the microorganisms in the biofilm are eliminated, the architecture of the biofilm survives and acts as a pre-formed matrix for renewal of the biofilm.

You'll hear from some product reps that shocking isn't necessary with certain products. We've not found this to be proven. Shocking your dental waterlines consistently purges out the regrown bacteria, restores a clean environment for continuous treatment, and ensures safe dental water.

Shock Every Week - Without using any dental water treatment (maintenance) products designed to be in your waterlines continuously, biofilm can re-attach and begin growth immediately after shocking your waterlines. Studies have shown that within five days, bacteria counts can grow to 200,000 CFU/mL. This method of maintenance requires consistent attention, and shocking less than once a week can put your patients and practice at risk.

Always check the manufacturer’s instructions for your equipment and shock product. Different chair manufactures suggest different shock protocols and different treatment products call for different techniques and frequencies. However, if someone tells you that you don't have to do any shock treatment because you use their magic product, think twice and ask yourself, is that a pro-active or re-active approach?

3. Poor Product Instructions for use!

Some products have instructions-for-use that suggest shocking is not necessary for safe waterlines, and some say that you only need to do shocking of lines when your “dip slides" or "HPC Samplers" detect contamination. Once again, ask yourself, is that a pro-active or re-active approach?

The data from this study proves otherwise. Here at The First Principle Group Ltd, we recommend that you don't ignore the best-known guidance, which is HTM01-05.

We also highly recommend using both a shock treatment and a continuous treatment, even if a sales rep says you do not need to.

As this is in line with the approved guidance:

"HTM01-05 P.6.86 Disinfection of DUWLs should be carried out periodically."

If you do that, you'll see it's never just twist or drop and you're done.

Also, to verify your protocol is sufficient, you could consider quarterly UKAS Accredited TVC Waterline Sampling. However, this is not a legal requirement and in line with the HTM01-05 "19.66 Apart from situations where there are taste or odour problems, microbiological monitoring for total viable counts (TVCs) is not considered to be necessary."

"19.68 All microbiological measurements should be by approved methods and/or be carried out by United Kingdom Accreditation Service (UKAS)-accredited laboratories. Dip slides are not acceptable."

PS. We have seen user manuals in Chinese only, being distributed in the UK 🤭

Very often, we hear practices saying this:

“We only use XXXX product and we don’t need any shock treatment. We also do dip slides and never have any problems..."

…. and then we see this:

Once again, apart from situations where there are taste or odour problems, microbiological monitoring for total viable counts (TVCs) is not considered to be necessary!

Use your senses! If it doesn’t look clean, it’s probably not clean and if dip slides don’t detect anything you should ask yourself why?

4. Underlying equipment issue

Lastly, and this is much less common, there can be an underlying equipment issue that can lead to poor failure rates. Sometimes, it can be as simple as an unknown toggle that switches some devices between sources (mains or independent water bottles). We've also seen some very old waterlines that have been building up biofilm for years. Other times, it can be dead legs that create stagnant water perfect for biofilm development that feed bacteria into the other lines and overwhelms the products. Sometimes it can be a filter or water distiller problem.


Each practice is different and should choose the right treatment protocol based on those unique needs. And again, each of these product types can be very effective. It's just that they can fail, too. Unfortunately, there is no one waterline maintenance magic product!

However, there are simple steps you can take to ensure your practice has a proven protocol.

  1. Balance Effectiveness with Convenience - review product instructions closely to see what is required but most of all familiarise yourself with HTM-01-05 and its requirements

  2. Ensure you have clear legionella management written scheme (the plan of action) that includes dental unit water lines management

  3. Make sure your written scheme is fully implemented, and all staff do what you ask them to do

  4. Combine Continuous treatment (ongoing maintenance) with Shock Treatment - always use both a shock treatment and a continuous treatment if you want consistently safe waterlines and show proactive management.

  5. Review your risk assessment, and if you use external consultants, makes sure they are competent and have sufficient knowledge and experience. Very often, we see dental practice legionella risk assessment's that don't even mention dental equipment, which makes this risk assessment inadequate.​

Best wishes,

Piotr Leszkiewicz - Independent Legionella Consultant

The First Principle Group Ltd

Health and Safety | Fire Safety | Legionella | COSHH & More


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