Drinking water hygiene
Drinking water: our most important foodstuff
Like other foodstuffs, drinking water also has a limited shelf life. If water stagnates in the pipes, also referred to as increasing water age, it can spoil. When stagnation occurs, drinking water absorbs substances from the installation materials as well as temperature from the environment. Both can lead to a changed drinking water quality that is harmful to human health. A temperature increase to over 25°C is particularly alarming, as microorganisms such as Legionella multiply explosively in lukewarm temperature ranges. A temperature of just <20°C is regarded as safe for cold water in many international standards and recommendations.
Therefore, especially operators of public buildings have to ensure hygienically perfect drinking water throughout the entire plumbing installation at all times. To meet this requirement, it is necessary to rule out the four main risks for a decrease of drinking water hygiene during design, installation and operation.
The four success factors that ensure perfect drinking water hygiene
Challenges in the design and implementation of drinking water hygiene
1. Flow
The pipes must be sized that occurring velocities generate shearing forces on the pipe walls during daily periods of high water consumption. The shearing forces minimize the build up of biofilm as adherence of particles is avoided.
Structural design influences piping network parameters that are relevant to hygiene
The structural design of a drinking water installation has a considerable influence on the piping network parameters that are relevant to hygiene such as wetted pipe surface and installation volume. To prevent stagnation and reduce water age in the pipes, the piping network must be designed with the objective to achieve as short as possible pipe connections to the tap. An example to minimize and equalize the length of pipe connections is a centralized incoming main supply into the plumbing installation.
Objective: short flow paths and minimal pipe volume
Short flow paths to the taps lead to a greater available pressure gradient in a piping network calculation. As a result, small pipe diameters can be selected. This means that higher flow velocities are achieved in all sections of the main distribution line when the drinking water installation is in use and therefore higher shearing forces come into effect on the pipe walls. Lower pipe contents with the same frequency of use at the taps also leads to a reduction of water age in the supply system. The exchange of water is therefore intensified and thus the average temperature level is significantly decreased. Comparative calculations show that the water content of a piping network can differ by up to 30% depending on the type of distribution concept.
Different distribution concepts
There are generally two different distribution concepts available for supplying drinking water to a building:
Horizontal distribution
In a horizontal distribution system, a main riser supplies water to a horizontal supply pipe in each floor of a building. The horizontal supply pipe of a floor is usually installed in the void of the corridor. All e.g. bathrooms are connected to this pipe to then supply the taps. Predominantly horizontal distribution systems are often found in buildings with large numbers of installations such as hospitals and hotels.
Vertical distribution
In residential buildings in contrast, drinking water is almost always supplied vertically, via risers. Here too, comparative calculations show that the choice of a horizontal or vertical distribution concept also has a big influence on the piping network parameters relevant to hygiene and not least also on the construction costs. Taking the same building geometry for example, the water content and internal surface of the piping network in a vertical distribution system is reduced by more than 20 percent as opposed to a comparable horizontal distribution system! The standby losses of the circulation system are also reduced by about 13 percent. The more extensive the piping network in a drinking water installation, the greater the described differences also become.
2. Temperature
In circulating hot water systems, the water temperature must be kept above 55°C everywhere, in the Netherlands for example, even above 60°C. The water content of a hot water installation, which cannot be held at this temperature must be minimised. The cold water temperature should be less than 25°C, and should preferably not exceed 20°C. If these temperatures cannot be maintained, this can lead to a change in drinking water quality that can be harmful to human health. A temperature increase to over 25°C is particularly alarming, as microorganisms such as Legionella multiply explosively in lukewarm temperature ranges. Therefore, especially operators of public buildings have to ensure hygienically perfect drinking water throughout the entire installation at all times.
Influence of internal heat loads
Heat sources such as hot water pipes of plumbing and heating systems and components of electrical and ventilation systems lead to a temperature increase of the cold drinking water pipes above 25°C within two hours of stagnation, even if the insulation is according to standards.
Influence of external head loads
High ambient air temperatures
High outside air temperatures can cause ambient air temperatures of more than 25°C in buildings without air conditioning. In the event of stagnation, cold water temperatures below 25°C can no longer be achieved as a result.
Water inlet temperatures
Where drinking water is sourced near ground level in the summer months, the temperature of water coming into drinking water installations is higher (>20°C), reducing the maximum tolerable stagnation time even more.
3. Water exchange
The design of a drinking water installation must result in a frequent water exchange in all parts of the building, particularly in the floor- and single supply pipes.
Microbial contamination through stagnation
Hygiene experts are constantly detecting inadequate drinking water hygiene in drinking water installations. The problems are present in both cold and hot water. Among experts, the primary cause of microbial contamination and therefore the change from drinking water to non-drinking water is said to be stagnation. The cause of stagnation areas can be old, unused pipes or sections of pipe which are temporarily not being used. These areas are therefore potentially a source of error in the drinking water installation.
Operators under obligation
The responsibility for the frequent exchange of water lies solely with the operator. It is recommended to separate unused pipes from the drinking water installation or to use all sections of the pipeline as intended. 'As intended' means that an adequate frequency of use and a frequent water consumption respectively has to be taken as the basis.
Change of usage behaviour
In many cases, the use of a building or usage behaviour has changed over a certain period of time. If the planned consumption of drinking water does not occur in sections of the piping installation as intended, the operation of the entire drinking water installation can be paralysed by germs. The originally planned operation as intended can then only be maintained by flushing measures.
Manual flushing measures
Manual flushing measures by opening and closing all taps affected means an increase of operating cost of the building. The additional operating and staff costs incurred as a result are seldom recognised and taken into account during the design phase. The consistent compliance with these flushing measures is as questionable as the objective being striven for, i.e. achieving the exchange of the entire water content. If just the measures on the flushing schedule already cause disproportionately high costs, then it can become extremely expensive if the manual implementation is not carried out carefully over time and hygiene deficiencies are detected when samples of the drinking water are tested.
4. Nutrient supply
The release of nutrients from materials must be reduced as far as technically possible. This also indirectly serves to prevent microbial growth both on the surface of the material and in drinking water.
Migration of material components encourages biofilm development
Longer contact between drinking water and materials (e.g. piping and valve) can cause parts of the materials to migrate into the drinking water, resulting in the concentration of nutrients. A combination of poor material quality, stagnation and unfavourable water quality encourages the strong development of biofilm, under the protection of which facultative pathogens can also multiply.
Reduction in the release of nutrients from materials
Complex components such as valves pose particular problems here. The microbiome controls a whole host of growth stimulating factors during stagnation phases. Since water is not removed in stagnation phases, the planktonic microorganisms that have made their way into the water are not diluted. The migration of nutrients from materials in contact with drinking water must therefore be reduced to the technically possible minimum. All materials must be tested for their suitability for drinking water usage.
KHS hygiene system
The KEMPER Hygiene System, KHS, prevents stagnation and the resultant impairment of drinking water quality. It ensures that fresh, hygienically perfect water is always available at every tap, taking into consideration efficiency and sustainability concerns. It offers every stakeholder, from the planner to the operator, from the installer to the end consumer, maximum security and safety in their daily contact with drinking water.
