For the purposes of the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland, backflow occurs when fluid flows in the opposite to the intended or normal direction of flow.
There are two types of backflow, back pressure and back siphonage.
The circumstances which could lead to backflow are a common occurrence across the UK. Contamination of public water supplies by backflow of fluids from customers premises is not theoretical, it is an ever present threat to water quality and public health.
Good design and the installation of suitable backflow prevention arrangements are key to avoiding backflow, which is why notification is so important.
Schedule 2 paragraph 15 of the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland require every plumbing system to incorporate protection against backflow. This is often referred to as point of use backflow protection. It can be provided by an air or tap gap arrangement or a mechanical backflow prevention device.
Backflow prevention arrangements and devices permitted under the regulations/byelaws need to be approved by the Regulator or alternatively authorised as a relaxation. Relaxations allow a water undertaker the discretion to accept an arrangement as preventing backflow.
Wherever practicable plumbing systems should be protected against backflow without the necessity to rely on mechanical backflow protection devices.
To be accepted as providing adequate backflow protection the backflow device or arrangement installed typically should:
Firstly be approved by the Regulator or a relaxation to authorise its use granted
Secondly be rated equal to or higher than the highest contamination risk (fluid category) downstream for the type of backflow (back pressure or back siphonage) a system is likely to be exposed to.
Thirdly be of an appropriate quality and standard.
As some backflow prevention arrangements and devices have operational limitations you should always check with the local water undertaker to make sure they are suitable for the intended application.
Please note: if high risk contaminants are likely to be present in a plumbing system, because these represent a greater risk to health, in addition to any point of use protection the water undertaker can also require the installation of zone or wholesite backflow protection.
Regulators Specification: Non-mechanical backflow protection | |||
Type | Description | Suitability by fluid category | |
Back pressure | Back siphonage | ||
AA | Air gap with unrestricted discharge above spillover level | 5 | 5 |
AB | Air gap with weir overflow | 5 | 5 |
AC | Air gap with vented submerged inlet | 3 | 3 |
AD | Air gap with injector | 5 | 5 |
AF | Air gap with circular overflow | 4 | 4 |
AG | Air gap with minimum size circular overflow determined by measure or vacuum test | 3 | 3 |
AUK1 | Air gap with interposed cistern | 3 | 5 |
AUK2 | Air gaps for taps and combination fittings (tap gaps) discharging over domestic sanitary appliances, such as a washbasin, bidet, bath or shower tray shall not be less than the following: Size of tap or combination fitting . Not exceeding G ½ Exceeding G½ but not exceeding G ¾ Exceeding G ¾
Vertical distance bottom of tap outlet above spillover level of recieving appliance 20 mm 25 mm 70 mm
| X | 3 |
AUK3 | Air gaps for taps or combination fittings (tap gaps) discharging over any higher risk domestic sanitary appliances where a fluid category 4 or 5 is present, such as:
Shall be not less than 20 mm or twice the diameter of the inlet pipe to the fitting, whichever is the greater | X | 5 |
DC | Pipe interrupter with permanent atmospheric vent | X | 5 |
Notes:
| |||
Regulators Specification: Mechanical backflow protection | |||
Type | Description | Suitability by fluid category | |
Back pressure | Back siphonage | ||
BA | Verifiable backflow preventer with reduced pressure zone | 4 | 4 |
CA | Non-verifiable disconnector with difference between pressure zones not greater than 10% | 3 | 3 |
DA | Anti-vacuum valve (or vacuum breaker) | X | 3 |
DB | Pipe interrupter with atmospheric vent and moving element | X | 4 |
DUK1 | Anti-vacuum valve combined with a single check valve | 2 | 3 |
EA | Verifiable single check valve | 2 | 2 |
EB | Non-verifiable single check valve | 2 | 2 |
EC | Verifiable double check valve | 3 | 3 |
ED | Non-verifiable double check valve | 3 | 3 |
HA | Hose union backflow preventer. Only permitted for use on existing hose union taps in house installations | 2 | 3 |
HC | Divertor with automatic return (normally integral with some domestic appliance applications). | X | 3 |
HUK1 | Hose union tap which incorporates a double check valve. Only permitted for replacement of existing hose union taps in house installations | 3 | 3 |
LA | Pressurised air inlet valve | X | 2 |
LB | Pressurised air inlet valve combined with a check valve downstream | 2 | 3 |
Notes:
| |||
Backflow occurs when fluid flows in the opposite to the intended or normal direction of flow. There are two types of backflow, back pressure and back siphonage.
Backpressure: occurs when the pressure downstream increases above that of the supply pressure, in effect pushing fluids backwards against the intended or normal direction of flow.
Back siphonage: occurs when the supply pressure drops below that of the system it is supplying creating a depressurisation or vacuum which pulls fluids backwards against the intended or normal direction of flow.
The type of backflow risk is dependent upon a number of factors. Good design and the installation of suitable backflow prevention arrangements are key to avoiding backflow, which is why notification is so important.
As the circumstances which could lead to backflow are a common occurrence across the UK, contamination of public water supplies by backflow of fluids from customers premises is not theoretical. It is an ever present threat to water quality and public health.
As there have been a number of serious contamination events across the UK water undertakers take their role in preventing such incidents very seriously. Where infringements are suspected or identified they will act, not only to protect water quality and public health, but also to support owners and occupiers of premises to meet their legal obligations.
Where contamination incidents occur, it is likely that enforcement action, including criminal proceedings, will be taken against those who fail to meet their legal obligations.
Water undertakers are legally required to ensure the drinking water they supply is wholesome. Contamination occurs when there is a change in water quality irrespective of whether or not it is harmful to health
Schedule 1 of the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland, classify the health risk posed by potential contaminants using a scale called fluid categories.
There are five fluid categories in total the lowest being 1 no risk the highest 5 a serious health hazard.
Fluid Category | Description | Example |
1
|
Wholesome (drinking) water supplied by the undertaker
|
water direct from a water undertaker’s main
|
2
|
Wholesome (drinking) water which has been changed either heated or altered in taste, odour or appearance
|
Hot water
|
3
|
Fluids posing a slight health hazard
|
low toxicity chemicals such as common disinfectants
|
4
|
Fluids posing a significant health hazard.
|
Toxic substances such as pesticides and environmental organisms
|
5
|
Fluids posing a serious health hazard
|
Pathogenic organisms, radioactive or very toxic substances such as faecal matter
|
As part of their statutory duty to enforce the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland, the local water undertaker will identify the level of backflow protection needed. This categorisation will be based on a number of factors including the highest downstream fluid category risk the fitting is or is likely to be subject.
It is in effect a barrier intended to prevent contaminated fluid flowing backwards.
Schedule 2 paragraph 15 of the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland require every plumbing system to incorporate protection against backflow. This is often referred to as point of use backflow protection. It can be provided by an air or tap gap arrangement or a mechanical backflow prevention device.
Backflow prevention arrangements and devices permitted under the regulations/byelaws need to be approved by the regulator or alternatively authorised as a relaxation. Relaxations allow a water undertaker the discretion to accept an arrangement as preventing backflow.
The regulator rates a backflow protection arrangement or device for suitability against contamination risk (fluid categories) and types of backflow risk - back siphonage or back pressure. They should always be accessible for inspection, maintenance and replacement.
Backflow prevention devices, are required to be corrosion resistant. For example, for metallic backflow prevention devices manufactured of gunmetal or other dezincification resistant materials. Dezincification water fittings are typically marked with a CR symbol.
Wherever practicable plumbing systems should be protected against backflow without the necessity to rely on mechanical backflow protection devices.
Irrespective of what a device is called, for the purposes of the water fittings regulations, byelaws in Scotland, the important factor is whether it provides protection against backflow.
There are two ways to verify the backflow protection capabilities of a device, both rely on satisfying a specification including performance testing. These are:
Conformity with BS EN 13959, the British Standard for both single and double checks valves, this also includes provision for fittings incorporating these devices.
or
Conformity with all of the tests from the Regulators Specification for fittings applicable to devices intended to be used as a single or double check valve.
Both of these routes include endurance tests intended to demonstrate the device continues to operate correctly over its lifetime.
Example of a non-return valve
Example of a check valve
The terms ‘check valve’ and ‘non-return’ valve are both commonly used to describe a device which allows flow from upstream to downstream but not the reverse. Only valves, or fittings incorporating devices, which conform with one of the above specifications can claim to provide backflow protection.
Those meeting the requirements of a single check valve can be used for fluid category 2 backflow protection, whereas those satisfying the requirements for a double check valve can be used for up to fluid category 3 backflow protection.
Supplied direct from mains
Where fire suppression systems are supplied directly from a supply or distributing pipe conveying water to be used for domestic purposes (i.e. water used for drinking, bathing, cooking or washing.) backflow protection should be installed on the fire suppression system pipework as close as is reasonably practicable to the point of connection to the supply or distributing pipe.
Fire suppression systems without additives are typically considered to a fluid category 2 risk. To be compliant a backflow protection rated to at least fluid category 2 must be installed on the branch supplying such systems as shown above.
Fire sprinkler systems using additives (e.g. rust inhibitors) are typically considered to be a fluid category 4 risk. To be compliant a backflow protection rated to at least fluid category 4 must be installed on the branch supplying such systems.
Supplied from dedicated storage
A storage cistern which is solely dedicated to supplying a fire suppression system is considered to be a fluid category 5 risk. To be compliant a backflow protection rated to at least fluid category 5 must be installed; typically a Type AB air gap is used for this purpose.
Furthermore, as the pipework supplying the storage cistern is considered to be a fluid category 2 risk, backflow protection rated to at least fluid category 2 must be installed as detailed above.
For further information about design and installation of fire suppression systems contact the local water undertaker.
Where a closed circuit (heating system etc) has been categorised by the water undertaker as a fluid category 3 risk, the installation of a compliant double check valve on the fill point connection to the supply/distribution pipe may be considered as acceptable backflow protection.
Where a fill point connection incorporates a “flexible hose connection”, when not in use it is good practice for the hose to be completely disconnected and removed. However, a partial disconnection, that is to say only detaching one end of the hose, may be acceptable providing the disconnection is made between the hose and the backflow prevention device on the supply/distribution pipe.
Please note: if the water undertaker has concerns about the likelihood of contamination, or the suitability of a double check valve - for example due either to age, operating temperature or pressure fluctuations – under schedule 2 paragraph 15(4) they can require the installation of additional backflow protection.
Point of use protection is backflow prevention provided at the point where water is being used. For example, at a tap, washing machine, WC or trough
Zone protection is a backflow prevention device or arrangement installed in addition to all existing point of use backflow prevention within a premises. Its purpose is to prevent backflow from one part of a plumbing system to another part of a plumbing system in the same property. For example, between different installations on one site. These are commonly found on farms, manufacturing sites and hospitals.
Whole site protection is a backflow prevention device or arrangement installed in addition to all other existing backflow prevention within a premises. Its purpose is to provide an additional level of protection to safeguard public water supplies to neighbouring properties.
Please note: the provision of zone and/or wholesite backflow prevention does not relax the requirement for any other required backflow prevention provision within premises.
Regulations & Byelaws which apply include but are not limited to:
Relevant guidance includes but is not limited to:
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