| To download the Word '.doc' version of this file, go to the Water Regulations page. |
Department of the Environment Transport and the Regions
Water Supply (Water Fittings) Regulations 1999
Guidance Document relating to
Schedule 1: Fluid Categories and
Schedule 2: Requirements For Water Fittings
[See Regulation 4(3)]
Downloaded Jan 2000 and converted to Word 97/2000 doc by Arrow
Valves Ltd.
The content is unaltered, formatting may differ at times.
RPZ requirements highlighted yellow
SECTION 6
Backflow
protection: Schedules 1 and 2
SECTION 6.1
Schedule 1: Fluid categories
Fluid category 1
Wholesome water supplied by a water undertaker and complying with the requirements
of regulations made under section 67 of the Water Industry Act 1991(a).
Fluid
category 2
Water in fluid category 1 whose aesthetic quality is impaired owing to-
a.
a
change in its temperature, or
b.
the presence of substances or organisms causing
a change in its taste, odour or appearance, including water in a hot water distribution
system.
Fluid category 3
Fluid which represents a slight health hazard because of the concentration of
substances of low toxicity, including any fluid which contains-
a.
ethylene
glycol, copper sulphate solution or similar chemical additives, or
b.
sodium hypochlorite (chloros and common
disinfectants).
Fluid
category 4
Fluid which represents a significant health hazard because of the concentration
of toxic substances, including any fluid which contains-
a.
chemical,
carcinogenic substances or pesticides (including insecticides and herbicides),
or
b.
environmental organisms of potential health significance.
Fluid category 5
Fluid representing a serious health hazard because of the concentration of pathogenic
organisms, radioactive or very toxic substances, including any fluid which contains-
a.
faecal
material or other human waste;
b.
butchery
or other animal waste; or
c.
pathogens from any other source.
SECTION 6.2
Schedule 2: Paragraph 15 Backflow prevention
15.
(1) Subject to the following provisions
of this paragraph, every water system shall contain an adequate device or devices
for preventing backflow of fluid from any appliance, fitting or process from occurring.
(2)
Paragraph (1) does not apply to-
a.
a water heater where the expanded water
is permitted to flow back into a supply pipe, or
b.
a vented
water storage vessel supplied from a storage cistern, where the temperature of
the water in the supply pipe or the cistern does not exceed 25°C.
(3) The device used
to prevent backflow shall be appropriate to the highest applicable fluid category
to which the fitting is subject downstream before the next such device.
(4) Backflow prevention shall be provided
on any supply pipe or distributing pipe-
c.
where
it is necessary to prevent backflow between separately occupied premises, or
d.
where
the water undertaker has given notice for the purposes of this Schedule that such
prevention is needed for the whole or part of any premises
(5) A backflow prevention
device is adequate for the purposes of paragraph (1) if it is in accordance with
a specification approved by the regulator for the purposes of this Schedule.
SECTION 6.3
Regulator's specification for backflow prevention arrangements and devices
S15.1
General interpretation of terms relating to backflow
prevention
"An air
gap" means a visible, unobstructed and complete physical air break between
the lowest level of water discharge and the level of potentially contaminated
fluid downstream (critical water level) within a cistern, vessel, fitting or appliance,
hereinafter called a receptacle, that:
a.
is not less than 20 mm or twice the internal
diameter of the inlet pipe whichever is the greater; and
b.
from which
water discharges at not more than 150 from the vertical centreline
of the water stream.
"Critical
level" means the physical or piezometric level of the fluid in any part of
the receptacle a minimum of two seconds after closing the water inlet, starting
from maximum water level.
"Maximum
level" means the highest physical or piezometric level of the fluid reached
in any part of the receptacle when operated continuously under fault conditions,
"Spillover
level" means the level at which the or fluid in
a receptacle will first spill over the top edge of a receptacle if the inflow
of water exceeds the outflow through any outlet and any overflow pipe.
"Tap gap"
means the vertical distance between the lowest part of a tap outlet and the spillover
level of the appliance or receptacle over which the tap discharges.
An "upstand"
means either one of two alternative arrangements of water fittings to prevent
backflow by backsiphonage:
|
Type A upstand |
An upward flowing supply or distributing pipe surmounted
by an anti-vacuum valve (Type DA), or an anti-vacuum valve combined with a single
check valve (Type DUK1), any part of the outlet of which is located not less than
300mm above the spillover level of an appliance. |
|
Type B upstand |
A branch pipe serving an appliance, where the height of any
part of the branch connection to the vented distributing pipe is not less than
300 mm above:
a.
the spillover level of the appliance;
or
b.
the
highest possible discharge point served by the vented distributing pipe, whichever
is the highest. |
"A verifiable backflow prevention device"
means a device, consisting of one or more backflow prevention elements, which
can be tested in-situ; usually achieved by the provision of test ports immediately
upstream, and between, the mechanical elements comprising the device.
S15.2
Interpretations of backflow prevention arrangements as listed in Table S6.1
"Type AA
- Air gap with unrestricted discharge" means a non-mechanical backflow prevention
arrangement of water fittings where water is discharged through an air gap into
a receptacle which has at all times an unrestricted spillover to the atmosphere.
"
"Type
AC - Air gap with vented submerged inlet and circular overflow" means a non-mechanical
backflow prevention arrangement of water fittings with a vented, but submerged,
inlet; the air gap being measured vertically downwards from the lowest point of
the air inlet to the critical level.
"Type AD
- Air gap with injector" means a non-mechanical backflow prevention arrangement
of water fittings with a horizontal injector and a physical air gap of 20 millimetres
or twice the inlet diameter, whichever is the greater.
"Type AF
- Air gap with circular overflow" means a non-mechanical backflow prevention
arrangement of water fittings with an air gap measured downwards from the lowest
point of the discharge orifice, which discharges into the receptacle, to the critical
level.
"Type AG
- Air gap arrangement with minimum size circular overflow" means a non-mechanical
backflow prevention arrangement of water fittings with an air gap; together with
an overflow, the size of which is determined by measure or a vacuum test.
"Type AUK1
- Air gap with interposed cistern" means a non-mechanical backflow prevention
arrangement consisting of a cistern with a Type AG overflow and an air gap; the
spill-over level of the receiving vessel (WC pan or other receptacle) being located
not less than 300 millimetres below the overflow pipe and not less than 15 millimetres
below the lowest level of the interposed cistern.
"Type AUK2
- Domestic tap gap" means the height of air gap between the lowest part of
the outlet of a tap, combination fitting, shower head or other fitting discharging
over a domestic sanitary appliance or other receptacle, and the spillover level
of that appliance, where a fluid category 2 or 3 risk is present downstream,
Type AUK3 - Higher
risk tap gap" means the height of an air gap between the lowest part of the
outlet of a tap, combination fitting, shower head or other fitting discharging
over any appliance or other receptacle, and the spillover level of that appliance,
where a fluid category 4 or 5 risk is present downstream,
"
S15.3
General interpretations of backflow prevention devices
as listed in Table S6.2
"Type BA - Verifiable backflow preventer with
reduced pressure zone" means a verifiable mechanical backflow prevention
device consisting of an arrangement of water fittings with three pressure zones
with differential obturators and that will operate when potential backflow conditions
obtain or there is a malfunction of the valve.
"
"Type DA
- Anti-vacuum valve (or vacuum breaker)" means a mechanical backflow prevention
device with an air inlet which is closed when water within the device is at or
above atmospheric pressure but which opens to admit air if a vacuum occurs at
the inlet to the device.
"Type DB
- Pipe interrupter with atmospheric vent and moving element" means a mechanical
backflow prevention device with an air inlet closed by a moving element when the
device is in normal use but which opens and admits air if the water pressure upstream
of the device falls to atmospheric pressure, the device being installed so that
the flow of water is in a vertical, downward direction.
"Type DUK1
- Anti-vacuum valve combined with a single check valve" means a mechanical
backflow prevention device comprising an anti-vacuum valve with a single check
valve located upstream.
"Type EA
- Verifiable single check valve" means a verifiable mechanical backflow prevention
device which will permit water to flow from upstream to downstream but not in
the reverse direction.
"Type EB
- Non-verifiable single check valve" means a non-verifiable mechanical backflow
prevention device which will permit water to flow from upstream to downstream
but not in the reverse direction.
"Type EC
- Verifiable double check valve" means a verifiable mechanical backflow prevention
device consisting of two verifiable single check valves in series, which will
permit water to flow from upstream to downstream but not in the reverse direction.
"Type ED
- Non-verifiable double check valve" means a non-verifiable mechanical backflow
prevention device consisting of two single check valves in series, which will
permit water to flow from upstream to downstream but not in the reverse direction.
"Type HA
- Hose union backflow preventer" means a mechanical prevention backflow device
for fitting to the outlet of a hose union tap and consisting of a single check
valve with air inlets that open if the flow of water ceases.
"Type HC
- Diverter with automatic return" means a mechanical backflow prevention
device used in bath/shower combination tap assemblies which automatically returns
the bath outlet open to atmosphere if a vacuum occurs at the inlet to the device.
"Type HUK1
- Hose union tap incorporating a double check valve" means a hose union tap
in which a double check valve has been incorporated into either the inlet or outlet
of the tap.
"Type L
- Pressurised air inlet valve" means an anti-vacuum valve or vacuum breaker,
similar to Type DA but suitable for conditions where the water pressure at the
outlet of the device under normal conditions of use is greater than atmospheric.
"Type LB
- Pressurised air inlet valve combined with a check valve downstream" means
a mechanical backflow prevention device comprising a Type LA anti-vacuum valve
and a single check valve located downstream.
SECTION
6.4
Guidance clauses relating to Schedule 1: Fluid categories; and Paragraph 15 of
Schedule 2: Backflow prevention
Guidance
General
G15.1 Except
where expanded water from hot water systems or instantaneous water heaters is
permitted to flow back into a supply or distributing pipe, every water fitting
through which water is supplied for domestic purposes should be installed in such
a manner that no backflow of fluid from any appliance, fitting or process can
take place.
G15.2 Avoidance
of backflow should be achieved by good system design and the provision of suitable
backflow prevention arrangements and devices, the type of which depends on the
fluid category to which the wholesome water is discharged. A description of fluid
risk categories is shown in Schedule 1 of the Regulations and some suggested examples
relating to the fluid categories are shown in Tables 6.1a to
e.
G15.3 The type
of backflow protection for a given situation is related to the fluid risk categories
downstream of the backflow prevention device.
G15.4 Schedules
of backflow prevention arrangements and backflow prevention devices, and the maximum
permissible fluid risk category for which they are acceptable, are shown in Table
S6.1
and Table S6.2
. Details of the arrangements and devices are shown in Table 6.2
and Table 6.3
.
G15.5 Wherever
practicable, systems should be protected against backflow without the necessity
to rely on mechanical backflow protection devices; this can often be achieved
by point of use protection such as a 'tap gap' above the spillover level of an
appliance. Minimum air gaps for different sizes of taps and applications are shown
in Table S6.1
.
G15.6 In cistern
fed systems secondary backflow prevention can often be achieved for appliances
by the use of permanently vented distributing pipes. See Figure 6.2b
.
G15.7 Mechanical
backflow protection devices which, depending on the type of device, may be suitable
for protection against backpressure or backsiphonage, or both, should be installed
so that:
a.
they are readily accessible for inspection,
operational maintenance and renewal; and,
b.
except for Types HA and HUK1, backflow
prevention devices for protection against fluid categories 2 and 3, they should
not be located outside premises; and,
c.
they are not buried in the ground; and,
d.
vented or verifiable devices, or devices
with relief outlets, are not installed in chambers below ground level or where
liable to flooding; and,
e.
line strainers are provided immediately upstream
of all backflow prevention devices required for fluid category 4. Where strainers
are provided, servicing valves are to be fitted upstream of the line strainer
and downstream of the backflow prevention device; and,
f.
the
lowest point of the relief outlet from any reduced pressure zone valve assembly
or similar device should terminate with a Type AA air gap located not be less
than 300mm above the ground or floor level; and,
Note: For information on the installation
and maintenance of reduced pressure zone devices (RPZ valve assemblies) see Installation
and Guidance Note No.
Appliances
incorporating, or supplied with water through, pumps
G15.8 Where pumped
showers, or other appliances supplied through or incorporating pumps, are installed,
care should be taken in positioning branches from distributing pipes.
Bidets
(including WCs adapted as bidets) with flexible hose and spray handset fittings
and with submerged water inlets
G15.9 Bidets
with flexible hose and spray handset fittings and/or water inlets below the spillover
level of the appliance, are a fluid category 5 risk and should not be supplied
with water directly from a supply pipe.
G15.10 Bidets
of this type may:
a.
be supplied with cold and/or hot water
through Type AA, AB, or AD backflow prevention arrangements serving the bidet
only; or,
b.
be supplied with cold water from an independent
distributing pipe serving the bidet only, see Figure
6.1a
; or a common distributing pipe serving the bidet and which may also serve a WC
or urinal flushing cistern only; or,
c.
be supplied with hot water from a water
heater, which is supplied from an independent distributing pipe, that serves the
bidet only, see Figure
6.1a
; or,
d.
where the bidet is at a lower elevation
than any other outlets or appliances, be supplied with water from a common cold
and/or hot water vented distributing pipe providing that:
i.
the elevation of the spillover level of
the bidet, if there is no flexible hose; or,
ii.
the
elevation of the spray outlet, with the hose extended vertically above the spillover
level of the bidet,
whichever is
the highest, is not less than 300 mm below the point of connection of the branch
pipe serving the bidet to the main distributing pipe serving other appliances.
Bidets
with water inlets above spillover level only
G15.11 Bidets
in domestic locations with taps or mixers located above the spillover level of
the appliance, and not incorporating an ascending spray inlet below spillover
level or spray and flexible hose, may be served from either a supply pipe or a
distributing pipe provided that the water outlets discharge with a Type AUK2 air
gap above the spillover level of the appliance. See Table S6.1
.
WCs and urinals
G15.12 The water
supply to a manually operated WC or urinal flushing valve may be derived either
from a supply pipe or a distributing pipe. The flushing valve should be located
above the WC pan or urinal and must incorporate, or discharge through, a pipe
interrupter with a permanent atmospheric vent; see
Shower heads
or tap inlets to baths, washbasins, sinks and bidets
G15.13 Except
where suitable additional backflow protection is provided, all single tap outlets,
combination tap assembly outlets, or fixed shower heads terminating over washbasins,
baths or bidets in domestic situations should discharge above the spillover level
of the appliance with a tap gap (Type AUK2) as scheduled in Table
S6.1
. For a sink in a domestic or non-domestic location, and for any appliances in
premises where a higher level of protection is required, such as some appliances
in hospitals or other health care premises, a tap gap (Type AUK3) is required,
see Table S6.1
.
Submerged inlets
to baths and washbasins
G15.14 Submerged
inlets to baths or washbasins in any house or domestic situation are considered
to be a fluid category 3 risk and should be supplied with water from a supply
or distributing pipe through a double check valve. Submerged inlets to baths or
washbasins in other than a house or domestic situation, and sinks in any location,
are considered to be a fluid category 5 risk and appropriate backflow protection
will be required.
Drinking water
fountains
G15.15 Drinking
water fountains should be designed so that the outlet of the water delivery jet
nozzle is at least 25 mm above the spillover level of the bowl. The nozzle should
be provided with a screen or hood to protect it from contamination.
Washing machines,
washer-dryers and dishwashers
G15.16 Household
washing machines, washer-dryers and dishwashers are manufactured to satisfy a
fluid category 3 risk. Where they are likely to be used in a non-domestic situation, appropriate
backflow protection for a higher fluid risk category should be provided.
Hose pipes for
house garden and other applications
G15.17 Hand held
hoses should be fitted with a self-closing mechanism at the outlet of the hose.
Commercial and
other installations excluding house gardens
G15.18 Any taps and fittings
used for supplying water for non-domestic applications, such as commercial, horticultural,
agricultural or industrial purposes should be provided with:
a.
backflow protection devices appropriate
to the downstream fluid category; and,
b.
where appropriate, a zone protection system.
G15.19
Soil watering systems installed in close proximity to the soil surface (that is,
where the watered surface is less than 150 mm below the water outlet discharge
point) for example, irrigation systems, permeable hoses etc., are considered to
be a fluid category 5 risk and should only be supplied with water through a Type
AA, AB, AD or AUK1 air gap arrangement.
House garden
installations
G15.20 Taps to
which hoses are, or may be connected and located in house garden locations are
to be protected against backflow by means of a double check valve. The double
check valve should be located inside a building and protected from freezing. (See Figure
6.3a
).
G15.21 Where,
in existing house installations, a hose pipe is to be used from an existing hose
union tap located outside a house and which is not provided with backflow protection,
either:
a.
the existing hose union tap should be
provided with a double check valve located inside the building; or,
b.
the tap should be replaced with a hose
union tap that incorporates a double check valve (Type HUK1); or,
c.
a hose
union backflow preventer (Type HA) or a double check valve should be continuously
fitted to the outlet of the tap.
G15.22
Where fixed or hand-held devices are used with hose pipes
for the application of fertilizers or domestic detergents the minimum backflow
protection provided should be suitable for protection against a fluid category
3 risk. Backflow protection against a fluid category 5 risk should be provided
where these devices are used for the application of insecticides.
G15.23 Where
mini-irrigation systems, such as porous hoses, are installed in house garden situations
only, a hose union tap with backflow protection in accordance with clauses G15.20
or G15.21 combined with a pipe interrupter with atmospheric vent and moving element
device (Type DB) at the connection of the hose to the hose union tap, or not less
than 300 mm above the highest point of the delivery point of the spray outlet
or the perforated surface of the porous hose, whichever is the highest, is acceptable.
See Figure 6.3b
and Figure 6.3c.
Whole site and
zone protection
G15.24 A whole-site
or zone backflow prevention device should be provided on the supply or distributing
pipe, such as a single check valve or double check valve, or other no
less effective backflow prevention device, according to the level of risk as judged
by the water undertaker where:
a.
a
supply or distributing pipe conveys water to two or more separately occupied premises
(whether or not they are separately chargeable by the water supplier for a supply
of water); or,
b.
a supply pipe conveys water to premises
which under any enactment are required to provide a storage cistern capable of
holding sufficient water for not less than 24 hours ordinary use. See Figure 6.2band
Figure 6.2c.
G15.25 The provision of zone or whole-site
backflow protection should be in addition to individual requirements at points
of use and within the system.
G15.26 Zone protection may be required in other than
domestic premises where particular industrial, chemical or medical processes are
undertaken.
Fire protection
systems
G15.27 Wet sprinkler
systems (without additives), first-aid fire hose reels and hydrant landing valves
are considered a fluid category 2 backflow risk Wet sprinkler systems with additives
to prevent freezing are considered a fluid category 4 risk.
G15.28 Fluids contained within large cylindrical
hydro pneumatic pressurised vessels are considered to be fluid category 4 risk.
G15.29 Where fire protection systems and drinking water systems are
served from a common domestic supply pipe, the connection to the fire systems
should be taken from the supply pipe immediately on entry to the building and
appropriate backflow protection devices should be installed.
|
Fluid category
1: |
|
Example
|
|
Table 6.1b:
Determination of fluid category 2 |
|
Fluid category
2: (a)
a change in its temperature; or |
|
Examples |
|
Table 6.1c:
Determination of fluid category 3 |
|
Fluid category
3 (a)
ethylene glycol, copper sulphate solution, or similar
chemical additives; or |
|
Examples
|
|
Table 6.1d:
Determination of fluid category 4 |
|
Fluid category
4 (a)
chemical, carcinogenic substances or pesticides (including
insecticides and herbicides); or |
|
Examples Primary circuits and central heating
systems in other than a house. House gardens Food processing Catering Industrial and commercial installations |
|
|
|
Table
6.1e: Determination of fluid category 5 |
|
Fluid
category 5 (a)
faecal material or other human waste; or |
|
Examples General Medical Food
processing Catering Industrial
and commercial installations Commercial
agricultural |
|
Note: The list of examples of applications
shown above for each fluid category is not exhaustive. |
|
Table 6.2: Details of backflow prevention
arrangements |
 |
|
Table 6.2:
Continued Details of backflow prevention arrangements |
|
Type |
Description of Device |
Installation |
 |
