62
TECHNICAL
Dead legs in water
reticulation
By Mark de Wet
Mark de Wet
Mark de Wet is the national
technical manager at
IOPSA. He is a qualified
plumber and registered gas
installer. He also sits on the
SABS technical committees
and working groups on
behalf of IOPSA and the
IOPSA National Executive
Board, as well as being a
PIRB inspector.
We have come across several plumbing installations over the
past few months that have issues regarding the dead legs of the
hot water piping.
With these installations, the plumber did not know
what is required to ensure that the pipework and
the dead legs in the installation are compliant.
Most problems occur in upmarket housing developments
where the architect has provided the design of the wet
services and the requirements of SANS 10252-1 have
not been considered, as it may affect the aesthetics of
the property.
The problem, however, surfaces once the property owner
has moved in and starts using the water installation
points, encountering a problem in the plumbing
installation. This could become a costly exercise to
repair or rectify the installation.
Another point to consider is that water conservation plays
a significant role in our lives — we all need to do our part
to save water. Understanding dead legs could be a key
point in a housing development to save water; yet, most
plumbers overlook it when completing the installation.
WHAT SANS REQUIRES REGARDING DEAD LEGS
Unless otherwise stated, the length of an unheated
pipe (dead leg) conveying water directly from a fixed
water heater to a terminal water fitting, or from the
point of take-off from a hot water circulating system to
a terminal water fitting, shall be such that the internal
volume of that pipe does not exceed 4ℓ.
Some dead legs
present a greater
risk than others
do. Some are
expensive to
correct, others
are not.
SANS 10252-1 also recommends the following
maximum lengths of dead-leg piping:
• Piping with an internal diameter of 19mm and
smaller: the dead leg should not be longer than
12m.
• Piping 19–24mm: the dead leg should not be
longer than 8m.
However, when working on an upmarket double-storey
property that is designed with a solar or heat pump
installation on the roof to supply the ground floor hot
October 2017 Volume 23 I Number 8
water points, one can easily require more than the
recommended length of pipe, thus causing an issue
when it comes to the requirements of the hot water
dead leg as per the standards.
HOW DEAD LEGS CAN AFFECT WATER
CONSERVATION
Apart from the volume limit, more than just the internal
volume of the pipe might have to be run to waste
before water of sufficient temperature emerges from
the tap, since the hot water has to heat up the pipe. For
example, a tap in a washbasin supplied by a 15mm-
diameter galvanised pipe 12m in length and discharging
at a rate of 6ℓ/min, would have to run for almost two
minutes before the temperature of the water entering
the basin is adequately heated. Thus, the volume of
water running to waste would be 6–12ℓ, whereas the
actual internal volume of the pipe is only 2.4ℓ.
LEGIONELLA BACTERIA IN DEAD LEGS
Piping with low or infrequent flows can be a breeding
ground for legionella bacteria. Although legionella
bacteria in dead legs can contaminate an entire
domestic water system, the presence of dead legs does
not necessarily mean there will be a legionella problem,
nor will removing the dead legs necessarily solve the
problem. Before removing a dead leg, consider the
benefits versus the cost.
Some dead legs present a greater risk than others do.
Some are expensive to correct, others are not. Hospitals,
nursing homes, hotels, office buildings, and other large
facilities should have an expert to evaluate the building
water systems and provide specific recommendations
for minimising stagnation.
It could be worth your while as a plumber or consumer
to educate yourself more regarding dead legs in a
plumbing installation and the standards’ requirements
to ensure a safe and eco-friendly plumbing environment
for us all. PA
www.plumbingafrica.co.za