Water & Wastewater Asia November/December 2022

FOCUS
BASICS OF
drinking water
hygiene
above 25°C and below 55°C, but in particular
30-42°C, must be avoided. The cold water
systems can often be overlooked and heat
transfer from the ambient air to the cold
water pipes can result in regular and longlasting
temperatures above 20°C. In the
German DVGW water information 90*, only
a temperature of below 20°C is considered
to be a safe temperature, which also
corresponds with many other international
standards, such as BS 8558* and HTM 04-
01*. In addition to avoiding stagnation and
limiting the food supply, it is necessary to
avoid the optimal temperature ranges which
positively condition the microbiome for the
growth of OPPPs.
By Chris Rhodes, associate director, Kemper UK & Ireland;
Frank Schmidt, market development engineer, Kemper
Group; Timo Kirchhoff, head of product management,
Kemper Group
Stagnation is probably the most critical
factor in the propagation of opportunistic
pathogens. National and international
regulation bodies such as the World Health
Organization (WHO), the European Centre for
Disease Prevention and Control (ECDC), the
Health and Safety Executive (HSE) and the
ISSO, widely agree that the primary factor in
the deterioration of water quality in buildings
is directly attributable to stagnation. Recent
studies from microbiome research show that
just 12 hours of stagnation is sufficient to
cause an increase in bacterial numbers*.
During periods of stagnation, prolonged
contact of drinking water with the piping
system materials such as the pipe, valves,
and fittings can lead to a concentration of
nutrients via migration from the material
components into the water itself. A
combination of poor material quality — such
as material that does not conform to BS EN
16421* or WRAS regulations* — stagnation,
and unfavourable water quality can promote
a strong biofilm development*, in which
opportunistic pathogens — characteristically
called opportunistic premise plumbing
pathogens (OPPPs) in international
literature — can multiply. Stagnation creates
propagation advantages for these OPPPs, as
there is no dilution or removal of the nutrients
or planktonic micro-organisms entering the
water body. Nutrient discharge from materials
in contact with drinking water must thus be
reduced as much as technically possible. It
is thus the responsibility of the designer and
installer that all materials have been checked
and approved for their “microbial suitability”
for the water installation.
In addition, the effects of environmental
temperature should be considered. During
stagnation phases, the temperature of the
water will adapt to the temperature of the
ambient air surrounding it, even with standard
insulation of the pipes. This becomes a
problem when the surrounding ambient
temperatures are in the optimal propagation
range of the pathogens. Low temperatures
provide the pathogens with poor or no
growing conditions. Temperatures close to
the growth optimum allow for rapid growth.
In legionella, atypical mycobacteria, but
also in P. aeruginosa, temperature ranges
INFLUENCE OF INTERNAL
HEAT LOADS
In installation areas, heat from hot water
pipes, heating circuits and other heat sources
such as electrical and ventilation technology
and the improvements in building thermal
performance, provide for air temperatures
which are significantly higher than 20°C. The
water content of a cold water pipe installed
here, even with insulation in accordance with
BS 5422, is heated to ambient temperature in
a short stagnation phase. With the installation
standards common today, it is expected that
after a period of stagnation, overheated cold
water with temperatures much higher than
20°C will flow from the tap for a significant
period of time. In accordance with BS 8558,
the cold water must be less than 20°C within
two minutes of running an outlet. If the
temperature of cold water is not below 20°C
within two minutes, the usability of the cold
water installation, according this regulation,
is no longer given. In addition to the abovementioned
internal heat loads and the impact
of improved building thermal performance,
incoming mains temperatures above 25°C
are expected to be more of a problem during
summer, due to higher temperatures from
climate change*.
To provide the consumer with compliant
cold water temperatures in the future,
conventional installation habits should first
WATER & WASTEWATER ASIA | NOVEMBER/DECEMBER 2022 35