Dental Unit Water Lines


What is a HPC water monitoring slide?

Described in the HSE approved code of practice, a HPC water monitoring slide – or red sampler – is a means of testing the microbial content of liquids.

Dipslides or samplers are the most commonly used method of measuring and monitoring biofilm within the dental setting.

What is the difference between red samplers and dipslides?

While the use of dipslides is not advocated by HTM01-05 Paragraph 19.68, as they are not sensitive enough for use as a test for drinking water quality nor do they detect legionella, they are quite capable of detecting the higher levels of bacteria associated with the presence of biofilms, so they could be used frequently as an inexpensive method of checking that gross bacterial invasion is not occurring.

Red samplers have been specifically designed to audit drinking water quality from dental units and clinical data shows them to be accurate to 1 colony forming unit (CFU).

In a recent clinical trial, the red samplers were compared to laboratory-based industry standard Total Viable Count (TVC) and were shown to be just as accurate.

Which one do you use?

While both red samplers and dipslides are both suitable for the testing of DUWLs the manufacturers of red samplers state “they are more sensitive than R2A”

If you are using Alpron, they recommend the use of red samplers to use with their product.


Samplers should be read seven days after performing the sampler test.

At this time, count any dots that have appeared on the sampler under a magnifying lamp for a closer look at the sampler.

Remember that size, colour, and shape of dots don’t matter, it is the number of colonies that need to be recorded.

Audit sheet

Sampler results should be recorded in your supplied sampler audit booklet.

Monitoring sampler results will allow you to notice trends and allow you to send off for your clean water certificate.


What process should I follow if my sampler fails?

Unmaintained chairs and lines?

The age of the chair and the lines can tell you something about the biofilm – if the lines have been in situ for a long time and have not been changed, the biofilm has had plenty of opportunity to develop and become solid.

Whether the tubing is flexible or brittle can also tell you if the biofilm has used the carbon in the tubing as a food source and has become ingrained in the tubes.


Frequency and usage is key to biofilm formation. Water movement in DUWLs is stagnant 85% of the time so if a chair is then only used for a couple of days a week this can contribute to biofilm formation.

Flushing twice a day as a minimum is a requirement to ensure fresh Alpron is in the lines.

Once mixed how long is the solution left before it is all used?

Keep the Alpron solution as fresh as possible –  ideally enough for a week is made up and used during the week.

You would not want to give someone a glass of water to drink that has been sat on the side for over a week.

Do you keep the bottles on at night? 

The Alpron protocol is a continuous application system which means the Alpron biocide needs to be in the system all the time and the bottle on the chair to stop any environmental contamination from entering the chair.

The HTM 01-05 advice regarding removing the bottle and air purging is to be followed in the absence of manufacturers guidelines. If no biocide is being used, air purging is the next best course of action although evidence shows this is not a suficient measure to stop biofilm formation in the DUWL.

The Alpron system is provided with clear manufacturers guidelines and this requests that the bottle stays on.

Are you mixing the Alpron up to the correct 1% solution?

The correct measurement must be adhered to, overdosing leads to foaming, underdosing leads to ineffective treatment. Use your measuring beaker to ensure that the right amounts are used.

What is your water source? (Tap, RO, Distilled?)

Alpron must be mixed with potable water – that is water that is less than 100 CFU per ml. RO is not sterile water – it must be tested!

Regular testing of the source water is recommended to get a trend.

Where do you keep mixed Alpron?

Store Alpron in your clean 5 ltr container, out of direct sunlight, and not in any extremes of temperature.

Holidays – is the chair left during holiday periods?

If the chair is not being used and brushed at least twice a day, then the use of Bilpron is recommended as it will hold the chair in stasis.

Bilpron can be used for any downtime exceeding 72 hours up to 3 months.

Are you cleaning your clean water bottle & 5 ltr storage containers? 

Regular cleaning – weekly – is necessary to ensure it does not become contaminated.

The clean water bottle should be emptied on Friday or used up and then decontaminated with BC San.

  1. Put the bottle back on the chair – fill with BC San solution and attach back to the bracket table – DO NOT PRESSURISE – and apply signage to the chair to warn that clean water bottle is undertaking treatment and should be removed and rinsed with water before being refilled with Alpron.
  2. Leave in place for the weekend and remove prior to use, flush with water, fill with Alpron solution and use as normal.
  3. Switch bottle for a clean alternative – if the practice does not want to put the bottle on the chair a pre-treated bottle should be switched onto the chair and the inlet tube and bottle thread should be cleaned with neat BC San. The bottle should be filled with BC San solution and left on the side over the weekend with clear signage to ensure it is emptied and flushed prior to use.

The 5 ltr container should be emptied on Friday or used up and then decontaminated with BC San. 3 x 100ml to 4700ml water and left with the lid on over the weekend.

Courses available via our online training site and additional information from our blogs

Maintaining Water Quality CPD Course click here >

Biofilm CPD Course click here > 

Isopharm Guidance Page – Dental Unit Water Lines click here >

ByRick Craven