The ABC of H2O

Simon Davies considers the role of water in infection control procedures in your dental practice, as well as looking at ‘point of use’ (POU) processing options, when potable (tap) water is appropriate for use, when it is not and why, and what can be done to bring water up to the standards required.

Learning outcomes

B, C

Aims and objectives

The aim of this article is to consider the importance of the water supply in the dental practice, looking at its sources, when potable water is appropriate for use, when it is not and why, and what can be done to bring water up to the standards required.

On completing this CPD article, the reader will:

  1. Understand how rain and ground water are processed in the UK to make it safe to drink
  2. Understand the limitations of its use in a healthcare setting
  3. Understand the requirements regarding colony forming units (CFUs) and dental unit water lines (DUWLs)
  4. Understand where water for dental unit water lines should be sourced from and how it can be processed.

To provide feedback on this article, please contact [email protected].

‘A’ brief history

We in the UK are lucky enough today to be able turn a tap and get water that is safe to drink. Clearly, this has not always been the case; evidence suggests that waterborne diseases were among the main causes of death in Ancient Greece, with Hippocrates, in about 350 BC, suggesting citizens should boil their water. There were limitations to this, as this ‘cleansing’ process could only tackle what the naked eye could see, what could be smelt, and what could be tasted. As we know all too well now, there are many bugs (organic material) and other impurities such as limescale or fertiliser residue/nitrates (inorganic material) that are too small to see without a microscope and that have no scent or taste.

Roll on a couple of thousand years and fatal epidemics were linked with poor sanitation and water quality, leading to London’s vastly improved sewer system in Victorian times, while in 1847 polluting the waterways was made a criminal offence in England.

‘B’ack to the 20th century: potable water

Effective water treatment was achieved in the 20th century with the development of industrial equipment able to process millions of gallons of water used by both domestic and business customers each day.

Water UK, a membership organisation that represents and works with the major water and wastewater service providers in England, Scotland, Wales, and Northern Ireland, describes the modern key steps for delivering safe water as follows:

  1. Rain is collected in reservoirs via rivers or streams (typically found in soft water areas, eg Wales, Scotland, Cumbria, etc), or water is filtered through the earth’s strata layers to form groundwater deep underground (hard water areas, eg southeast England, London, etc)
  2. The water is screened to remove large objects, for example branches and leaves
  3. Particles are then removed via a filtering process, using sand. Some water works add ozone, carbon and/or ion exchange to remove microscopic and dissolved particles from the water
  4. Finally, a small amount of chlorine is added to eliminate any remaining bacteria and other organisms.

Among the most commonly found bacteria in drinking water are Pseudomonas, Sphingomonas, Methylobacterium, Aeromonas and Acinetobacter. This is a potential problem because, for example, Methylobacterium species exhibit resistance to chlorination and are classified as ‘opportunistic pathogens’ in dental unit water lines (Tsagkari et al, 2017).

‘C’olony forming units

EU Directive 98/83 (amended in 2015) states that the European standard for drinking water should be fewer than 100 CFUs in the potable supply. For water used in DUWLs, the current recommendation for England, Wales and Northern Ireland is 100 to 200 CFU/ml (as detailed in section 6.79 of HTM 01-05),  even after any POU filtration is used.

However, extraneous factors can suddenly push this figure up in some clinical situations, often as a result of internal conditions being ideal breeding grounds for pathogens: warmth, moisture, extended periods of inactivity (stagnation), dead-legs in plumbing layout and processed water that has had the chlorine removed. Research has revealed that bacterial counts in DUWLs can be enormous, with one study on demonstrating an incredible colony size of 19,500 CFUs.

It does not necessarily follow that exposure to pathogens will lead to disease; rather, it depends on the virulence and dose of microbes, and the robustness of the host’s immune system (Willey, Sherwood and Woolverton, 2014). However, those who are immunocompromised – for example, the elderly and those with HIV, smokers, diabetics, and alcoholics – may become infected by the likes of Legionella and Pseudomonas (Willey, Sherwood and Woolverton, 2014; Pankhurst, Scully and Samaranayake, 2017).

This is not conjecture; a California-based dentist became seriously ill after contracting Legionnaires’ disease, while, more recently, an Italian elderly woman died as a result of contamination via DUWLs at her dental practice (Pankhurst, Scully and Samaranayake, 2017).

‘D’iscussing water sources

Purified water is integral to the smooth running of two key pieces of dental equipment – namely, dental chairs and autoclaves.

This begs the question – from where should water for DUWLs (chairs) be sourced and how can this be achieved? The answer depends on your dental chair design, with two types available. ‘Mains fed’ chairs require a permanent connection to potable water and thus have a constant supply feeding the waterlines. More commonly in the UK, ‘self-contained’ dental chair systems have independent water reservoirs and require reverse osmosis (RO) or distilled water, to adhere to HTM 01-05 ‘best practice’ advice (section 6.84).

Cross-infection specialist Caroline Pankhurst et al (2017) have this to say on the subject: ‘Although water can be taken from the mains supply (potable water), to achieve the specified water quality, dental units are usually fitted with a separate water reservoir that is independent of the public water supply. This allows dentists to have better control over the microbial quality of the water used in patient care by the addition of biocides and other methods to control contamination. In addition, they act as a type A air-gap, a physical gap that prevents back siphonage of contaminated water into the mains supply. Reservoir water bottles are recommended to be filled with freshly produced (less than 12 hours old) reverse osmosis or distilled water. These purified waters are not sterile but are unlikely to contain NTMs [Nontuberculous Mycobacteria] and pseudomonads found in potable tap water.’

Furthermore, technical guidance HSG274 (part 3) of the L8 Approved Code of Practice recommends that, ‘storage bottles should be cleaned, rinsed with RO or distilled water, drained and inverted overnight.’

As for autoclaves (steam sterilisers), section 4.11 of HTM 01-05 states: ‘Each sterilizer …should be filled, at least daily, using distilled or RO water’.

‘E’asy solution!

For the easiest and safest solution, reverse osmosis is increasingly used by dental practices of all sizes, right up to the largest dental corporates on ‘self-contained’ systems. So, what is reverse osmosis, or RO?

In essence, an RO system offers a fast, easy and cost-effective way of providing as much dental grade purified water as practices need for dental chair water bottles and autoclaves, at the turn of a tap. Distillers, by contrast, involve boiling water to form steam and then cooling it down again before use, resulting in lots of heat being generated and electricity being used, whilst bottled water needs lots of heavy lifting and storage by over-stretched dental staff. Both are often more expensive per litre when all costs are taken into account, compared to RO according to

The simple procedures employed by some RO systems, for instance those available from Cleancert, are designed to ensure the dental team can remove both organic (eg bacteria) and inorganic matter (eg calcium carbonate) found in all DUWLs quickly and easily, without the expense of calling out an engineer.

Easy to install and easy to maintain – so why not make your dental water supply for your chairs and autoclaves as easy as ABC with an RO system?


Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption. Official Journal of the European Communities 1998; 32 (updated in 2015)

Decontamination Health Technical Memorandum 01-05: Decontamination in primary care dental practices. Department of Health 2013

Legionnaires’ disease: Technical guidance. Part 3: The control of legionella bacteria in other risk systems; 2013: 6

Pankhurst CL, Scully C and Samaranayake L (2017) Dental unit water lines and their disinfection and management: a review. Dental Update 44: 284-92

Tsagkari E, Keating C, Couto J and Sloan W (2017) A keystone Methylobacterium strain in biofilm formation in drinking water. Water 9(10): 778

Willey JM, Sherwood L and Woolverton C (2014) Prescott’s Microbiology. McGraw-Hill Education; Edition 9

CPD questions

This article is equivalent to one hour of enhanced CPD. To answer the questions and obtain a certificate, please visit

1. What dental equipment should use reverse osmosis (or distilled) water, as stipulated in HTM 01-05
(2013 edition)?

a) Hand wash basins

b) Autoclaves and suction pump systems

c) Dental chairs and autoclaves

d) Drinking water fountains

e) Eyewashes

f) Water coolers

2. As a final treatment step, within the UK, what is added to tap water to eliminate bacteria and other organisms?

a) A small amount of ozone

b) A small amount of chlorine

c) A small amount of carbon

d) A small amount of fluoride

e) A small amount of calcium

f) A small amount of sodium hydroxide

3. What bacteria species has exhibited resistance to chlorination and are classified as ‘opportunistic pathogens’ in DUWLs?

a) Aeromonas

b) Sphingomonas

c) Pseudomonas

d) Methylobacterium

e) Cryptosporidium

f) Hexamitidae

4. As detailed in section 6.79 of HTM 01-05, the current CFU recommendation for England, Wales, and Northern Ireland for DUWLs is what?

a) Fewer than 1,000 CFU/ml

b) 100 to 500 CFU/ml

c) 100 to 250 CFU/ml

d) 50 to 100 CFU/ml

e) There is no recommendation

f) 100 to 200 CFU/ml

To help you and your team achieve HTM ‘best practice’ easily and cost-effectively, please visit, email [email protected] or call 08443 511115, for further information on the full range of proven, innovative dental infection control and water purification products available from Cleancert.

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