Dental unit waterlines (DUW) are often just a few millimetres in diameter.
Water flows slowly or not at all and is often warmed up to body temperature. These are perfect conditions for the growth of a so-called biofilm layer. The biofilm is a slimy layer of minerals, algae and fungi. Even in brand new dental waterlines these layers form within a couple of weeks.

The suspicion that the majority of Dutch dental offices uses contaminated water was confirmed on March 25 -2001. At that time the Dutch Journal for Dentistry published ( NT 56 Annual nr. 6 page 224 ) the results of a university study carried out by ACTA university students.
Fifty Amsterdam dentists volunteered to explore the safety of their dental unit water supplies in that study.
The outcome was alarming : of 50 offices only 2 turned out to be safe.


Most dental equipment is directly connected to the main watersupply, but this does by far not mean that dental water is as safe as your tap water is.

Watersuppliers are obliged to deliver water that contains no more than 200 CFU's per cubic millimetre. CFU's are Colony Forming Units (units being micro-organisms and a cubic millimeter is about a small thimble). These quantities are very low, but within dental installations they meet heavenly breeding grounds and they will grow like hell.

Some dental installations even contain small boilers to bring up dental water to an agreeable temperature for the patient. These boilers are fatal from a bacteriological point of view. It's really asking for trouble and they should be banned.

Legionella is not unfrequently found in dental unit waterlines (DUWL).

Fifty percent of Dutch dentists and eighty percent of their dental nurses developed antibodies against Legionella, meaning they must have been in close contact with the bacterium ( NT 56/6/2001).

The picture showing legionella in PVC pipe is from the Special Pathogen Laboratory, Pittsburgh PA, USA and used with their permission. ( also see links )


Remember how a stopped and spinning high-speed turbine works like a pump?
This is one example of passive suck-back.


It is inconvenient if an instrument drips on the nice marble floor when it stops. Suck-back is an invention that prevents instruments from dripping by sucking some water back into the instrument's watertube.

Suck-back is dangerous and should be forbidden.

Once inside dental water lines bacteria are very hard to get out. When removed (by steaming or by chemicals) they are back within two weeks.


It's a well kept secret that dental waterlines often contain ten thousand times more micro-organisms than officially allowed. Water suppliers garantee 200 CFU; dental units waterlines often exceed 100.000 CFU.