CATEGORIES OF RISK
The water regulations published in 1999* take a new approach to backflow in that they look at different
categories of risk. The installer must assess the risk from the various categories of fluid in adjacent appli
-
ances before determining the level of backflow protection required for a particular installation.
Figures 3 &
4
describe the protection required in various installations.
CATEGORY 3 RISK
Water in a shower tray, basin or bathtub is considered to be a fluid category 3 risk which is a fluid which
represents a slight health hazard if it were to find it’s way back into the supply pipe. For this reason it must
not be possible for any flexible shower head to be able to enter any adjacent washbasin, bath or shower
tray unless appropriate protection is employed.
(See Figure 3)
. If it is desired to allow the hand spray to
7
zone of backflow
risk for longer
hose
spill
over
level
bath or shower tray
25mm minimum air gap
required if check valves are
not fitted
spill over
level
washbasin
zone of
backflow risk
for shorter
hose
no additional
backflow protection
required
cold and hot water supplies
to shower valve will need
additional check valves on each
service if longer hose is fitted
zone of backflow risk
for restrained hose
which is longer than
system design hose
- not permitted -
zone of backflow
risk for unrestrained
hose
zone of backflow risk
for restrained hose
w.c.
spill-over
level
shower tray
or bath tub
bidet
w.c.
spill-over
level
restrained hose giving
the 25 mm air gap is
permitted
25mm
minimum
unrestrained
hose would
not be
permitted
be used inside say a bathtub or a basin
it is essential that double check valves
be fitted to the inlet on both hot and cold
supplies to the thermostatic valve. Alter
-
natively single check valves can be fitted
at the inlets and an additional check valve
should be fitted in the valve outlet.
No check valves need be fitted if the hand
spray is prevented from reaching closer
than 25mm of the spill over level of any
such fixture.
CATEGORY 5 RISK
Water in a Sink, WC or Bidet is considered
to be a fluid category 5 risk which is a fluid
which represents a serious health hazard
if it were to find it’s way back into the
supply pipe. For this reason it must not be
possible for any flexible shower head to
be able to enter any adjacent Sink, WC or
Bidet. If the flexible hose to be fitted could
reach into any such vessel, the require-
ments to the system design are so one-
rous it is better not to fit a flexible. Rather,
a fixed overhead showerhead should be
considered.
(See Figure 4)
.
It will also be seen that this risk could
change should the hose be taken out of
the restraining device or should a longer
replacement hose be fitted at a later date.
Installers and householders are advised to
take account of these factors when fitting
replacement hoses.
For pumped applications the pipe supply
-
ing the pump must not in addition supply
an ascending spray bidet.
Fig. 3 Backflow risk from a fluid category 3
Fig. 4 Backflow risk from a fluid category 5
3 WATER REGULATIONS
