Biofilms – the underestimated danger
Carelessness and ignorance about drinking water hygiene cause many cases of illness.
If water is left to stagnate in water systems for longer periods of time, bacterial coatings, so-called biofilms, form on the inside walls of tanks and pipes. Bacteria can break away from these and then multiply in the water. Apart from making the water taste unpleasant, this is also a danger to health.
1. Stagnation in water systems
Stagnation occurs when no water is being taken out of pipes or tanks. If this stagnation lasts for any length of time, the quality of the water in the tank, pipes and fittings is so impaired by bacterial growth that it is no longer considered safe to drink. Particularly at risk, in this instance, is the water in pipes in yachts, caravans and motor homes because - unlike in the public water supply - the water is not being continuously run off. Poor design and installation can also create additional stagnation problems.
2. Consequences of stagnation
As a result of stagnation, the following individual changes can occur in water (hot and cold water), although in practice they are usually superimposed upon each other, leading to complex situations. In most cases they are not harmful to health but affect the use, availability and palatability of the water. They result in changes to the smell, taste, appearance and temperature of the drinking water, all due to stagnation.
Example of materials
Polyester or rubber water tanks and soft PVC hoses can adversely affect the taste of the water, if it is left to stagnate in them, rendering it unfit for human consumption. If water stagnates in metal pipes or in plastic pipes and hoses not approved for drinking water use, it can leach substances out of the respective pipe material (e.g. lead, copper, plasticiser). Health hazards and even poisoning may result if the stagnant water is heavily contaminated with undesirable components from the materials making up the tank, pipes and fittings.
Example of bacteria
When stagnation results in microbial activity, metabolic products are released into the water. These can cause strong odours (e.g. rotten eggs) and affect the taste so that the water is undrinkable. Example of temperature changes When taps are not being continuously used (jetty standpipes, filling stations), the stagnant water that has been standing in the pipe comes out warm and has to be left to run for a long time before it is cold enough to drink. If the stagnation conditions are bad enough, they allow pathogenic microorganisms to grow and these are detrimental to health.
Example of Legionella
When taps at jetty facilities or filling stations are not continuously used, the water comes out warm (30 - 50° C) due to stagnation in the pipe as well as climatic conditions. These are the perfect conditions for various microorganisms - such as Legionella (rod-shaped bacteria) - to colonise the water system and multiply en masse. Just breathing in contaminated aerosols (for example, in the shower) can cause serious lung infections (legionnaires disease).
Example of helicobacter
The stomach bacterium helicobacter pylori is able to grow in the biofilms in water pipes. It can cause stomach problems and even cancer. It is true that the bacterium is killed by chlorinated water but that does not prevent it from surviving in the biofilm. There is then a possibility that it might be flushed out and so find its way directly into the stomach via drinking water that has not been disinfected.
3. Materials for water systems
Plastics have to be licensed for food use (quality label), must have been processed in compliance with the Plastics Commission recommendations and may not release any substances that are detrimental to health or negatively affect the drinking quality of the water, if it stagnates in them.