9
9
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
appliances 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 washba
-
sin, bath or shower tray unless appropriate protection is employed.
(See Figure 3)
. If it is desired to
allow the hand spray to 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. Alternatively single check
5
WATER REGULATIONS
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
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 con-
sidered 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 requirements
to the system design are so onerous 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
supplying 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
