HEALTH AND SANITATION
Air gap
a. An air gap is required as part of a top-up
system for backflow prevention (zone
protection).
b. Air gaps shall be designed and installed
in accordance with applicable national/
provincial/ local codes and regulations.
For guidance purposes only, the following
guidelines are provided.
• The gap must be unobstructed –
mechanical supports, fixing the potable
water supply pipe to the top-up drainage
pipe or other components located at or
between the potable water supply pipe
and the top-up drainage pipe, are not
permitted.
• The air gap must be located in an area
where it can be observed and inspected.
• The air gap must be installed at a height
above the flood level rim (overflow) of
the rainwater storage tank. If not, there
is a risk that rainwater will back up in the
top-up drainage pipe and overflow from
the air gap.
• The air gap height must be at least
25mm [1 in.] or twice the diameter of
the water supply pipe.
c.
Splash and water damage prevention:
i. To prevent make-up water from
splashing at the air gap, install the
following:
•
flow restrictor, installed upstream
of the solenoid valve; and/or
•
aerator, installed where the
potable water supply pipe
terminates; and/or
•
extended length of vertical pipe
with the end of the pipe cut at
an angle no less than 45° (to
produce laminar flow), installed
where the potable water supply
pipe terminates above the air gap.
ii. To prevent water damage to rooms
where the air gap is located:
•
locate air gaps near a floor drain;
•
install an overflow on the top-up
drainage pipe, located downstream
of the air gap, to direct excess
make-up water to the sanitary
sewer (where permitted by local
authorities); and
•
appropriately size and slope the
top-up of the drainage piping.
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d. Make-up water flow rate
i. To ensure RWH system operation
during top-up, the following
measures are recommended:
•
the flow rate of make-up water
should be equivalent to that of the
maximum flow rate of the rainwater
supply pump; or
•
the water level sensor(s) should
be configured to provide a sufficient
reserve volume in the rainwater storage
tank (where said reserve volume shall
be equivalent to that of the average daily
rainwater demand for the RWH system).
MAINTENANCE
Following the installation of the RWH system,
if the make-up system does not operate, or if
it operates when it should not (for example,
tops-up the tank when there is a sufficient
quantity of rainwater in the tank):
a. ensure that the proper control
equipment was selected and arranged
in accordance with the Design and
installation guidelines provided;
b. visually examine the RWH system .
Backflow preventer testing and maintenance
according to manufacturer’s instructions.
If the make-up system is operating properly, it
is recommended that it still be inspected once
every six months to:
a. verify that the float switch wires are not
tangled with other float switches, the
pump or other objects in the tank;
b. remove any dirt and/or debris that have
accumulated on the float switches, as
necessary; and
c. observe the make-up system while
operating to ensure that water is not
overflowing from the top-up drainage
pipe at the air gap or discharging from
the backflow preventers. If any water
is leaking or discharging, refer to the
troubleshooting instructions above.
While inspecting, cleaning or repairing the
make-up system, follow all necessary safety
precautions, such as disconnecting the power
supply, when necessary. PA
In the next article we look at overflow
provisions.
June 2019 Volume 25 I Number 4