Finnish tap water is undoubtedly among the cleanest in the world. However, water quality can change on its journey from the waterworks to the tap. One influencing factor is the material used in the pipes.
Biofilms – communities of microorganisms that attach to the pipe surface – naturally form on the inner surfaces of domestic water pipes. Biofilms are not always a bad thing, but under favourable conditions they can provide a protective environment for harmful bacteria.
Bacteria living in biofilms can withstand chlorination up to hundreds of times better than those freely floating in water. In suitable conditions, microbes from the biofilm may also begin to multiply in the water itself, which can weaken the microbiological quality of drinking water.
Differences between pipe materials in biofilm formation
At SAMK’s WANDER research centre, the growth of biofilms on new pipe surfaces was monitored over a period of 16 months. The materials studied were PEX, copper and stainless steel.
The result was clear: significantly more biofilm accumulated in PEX pipes than in metal pipes. One suspected reason is that new plastic pipes may initially release organic compounds that serve as nutrients for microbes.
Stainless steel performed best in the study: it does not provide an easy surface for microbial attachment or additional nutrients. Copper ranked between the two. Its natural antimicrobial properties help to inhibit microbial growth, although the effect decreases over time.
When does the risk increase – and what can residents do?
The study also found that the amount of biofilm varies clearly with the seasons. During warmer months, more biofilm developed, particularly in plastic pipes. If a building is used less during summer – for example, due to holidays – and water remains stagnant in the pipes for longer than usual, the microbiological risk increases.
There is no need for concern in a typical household, as Finnish drinking water is generally safe and its quality is carefully monitored by water utilities. In addition, running the tap briefly before use is a simple way to improve the safety of drinking water.
In special settings such as hospitals, care homes or the food industry, the choice of pipe material can be one way to manage microbiological risk. In building maintenance, it is worth remembering that summer and long periods of low use are times when greater attention should be paid to flushing systems and maintaining pipework.