UK Dentists
The UK performs relatively well on governance and guidance, tough recent nationwide published prevalence data is hard to find.
In England, dental practices are expected to follow HTM 01-05, which includes a dedicated chapter on hot and cold water systems and dental unit water lines.
The CQC’s updated 2025 guidance also makes it clear that practices must not treat dental water safety as just a paper exercise; it explicitly warns that contaminated waterlines can expose staff and patients to harmful aerosols and that vulnerable patients may be at increased risk.
South Africa
High contamination and weaker regulation
Compared with South Africa, for example, the difference is obvious. The South African study specifically notes that the country has no explicit national requirements for water quality supplied to dental chair units or for DUWL disinfection protocols.
United States
Taking the issue seriously
But the systems are organised differently from the UK.
The US position is strongly shaped by CDC recommendations and ADA guidance, including a current ADA infection prevention guide that now includes a dedicated chapter on dental water quality.
Morocco
Extremely high contamination rates
In Morocco, a 2025 two-year study at a university dental centre found that 100% of DUWL output samples were above CDC and ADA thresholds, even though the input water was free of contamination.
Levels were especially high before the start of the working day and at the start of the week, which strongly suggests the role of stagnation and in-line contamination rather than poor source water alone.
Kuwait
Strict controls, getting 1 in 6 contamination
Kuwait’s 2025 nationwide study gives a slightly different but equally useful picture. Using 3,290 water test results from primary healthcare centres, researchers found overall contamination in 16.8% of samples, with P. aeruginosa in 1.3%. That number sounds lower than some other studies, but Kuwait was using a very strict threshold of more than 100 CFU/mL or the presence of certain specific organisms. The researchers concluded that one in six samples still exceeded Kuwait’s safety threshold and called for stronger disinfection, preventive maintenance and staff training.
France
New equipment just as contaminated
France offers another important lesson: this is not only a problem in older clinics or lower-resource settings.
A 2024 hospital study found that all 17 newly installed dental chairs were contaminated by viable aerobic bacteria before shock disinfection, including P. aeruginosa. Even after shock disinfection, 24% remained contaminated by aerobic bacteria and one unit still had P. aeruginosa.
In other words, contamination can begin very early and should not be assumed away simply because equipment is new.
Iran
Consistently high contamination in academic studies
Iran appears frequently in systematic reviews of DUWL research because several studies from dental schools have reported very high microbial loads.
Typical findings include:
- Bacterial counts far above recommended limits
- Frequent detection of Pseudomonas species
- Evidence of biofilm inside dental waterlines
- Large differences between input water quality and dental unit output
Some Iranian studies have reported contamination rates above 70–90% of tested dental units, depending on the threshold used.