Glossary

 

AIM

A method of installation approved by the water undertakers (water suppliers) under Regulation 4 of the Water Supply (Water Fittings) Regulation/Scottish Water Byelaws. Regulations 4 (6) & 12 of the Water Supply (Water Fittings) Regulations and/or Scottish Water Byelaws.

Air gap

"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

Approved contractor

A person who– (a) has been approved by the water undertaker for the area where a water fitting is installed or used, or (b) has been certified as an approved contractor by an organization specified in writing by the regulator. Interpretation given in Part 1: Preliminary of the Water Supply

Backflow

Flow upstream, that is in a direction contrary to the intended normal direction of flow, within or from a water fitting. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Backflow Prevention Arrangements

Follow the links below to get definitions of each of the recognised backflow prevention arrangement. Air gap Tap gap Type AA air gap – air gap with unrestricted discharge Type AB – Air gap with weir overflow Type AC – Air gap with vented submerged inlet and circular

Backflow Prevention Devices

Please follow the links below to see definitions of each backflow prevention device: Type BA – Verifiable backflow preventer with reduced pressure zone Type CA – Non-verifiable disconnector with different pressure zones Type DA – Anti-vacuum valve (or vacuum breaker) Type

BS 6920

A British Standard in four parts, last updated in 2014, entitled ‘Suitability of non-metallic materials and products for use in contact with water intended for human consumption with regard to their effect on the quality of the water’. It is a requirement that all non-metallic materials

CAS registration number

A universally used unique numerical identifier allocated to a chemical substance by the Chemical Abstracts Service (CAS). A CAS Registry Number itself has no inherent chemical significance but provides an unambiguous way to identify a chemical substance or molecular structure when there are many

Cistern

A fixed container for holding water at atmospheric pressure. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Combined feed

A cistern for supplying cold water to a hot water system without a separate expansion cistern Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Concealed fitting

A water fitting which – is installed below ground; passes through or under any wall, footing or foundation: is enclosed in any chase or duct; or is in any other position which is inaccessible or render access difficult [Refer to Water Regs UK publication ‘Schedule 2 paragraph 7 explained’ for

Contamination

Includes any reduction in chemical or biological quality of water due to a change in temperature or the introduction of polluting substances. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Critical level

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. Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: terms relating to

Distributing pipe

Any pipe (other than a warning, overflow or flushing pipe) conveying water from a storage cistern, or from hot water apparatus supplied from a cistern and under pressure from that cistern. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water

Domestic use

Domestic use is defined in section 218 of the ‘Water Industry Act 1991’: 218. Meaning of “domestic purposes” in relation to water supply. 218.─(1) Subject to the following provisions of this section, in this Act references to domestic purposes, in relation to a

Economic Regulators

Various regulatory bodies are responsible for ensuring that water companies provide good quality service and value for money. England & Wales Ofwat (The Water Services Regulation Authority) is the economic regulator of the water and sewerage sectors in England and Wales. They make sure that the

EEA state

A State which is a contracting party to the EEA Agreement. Interpretation given in Part 1: Preliminary of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

European Technical Approval

Means a favourable technical assessment of the fitness for use of a construction product for an intended use, issued for the purposes of the Directive by a body authorised by an EEA State to issue European technical approvals for those purposes and notified by that State to the European Commission.

Expansion valve

A pressure-activated valve designed to release expansion water from an unvented water heating system. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Fluid Categories

Fluid category Means a category of fluid described in Schedule 1 of the Water Supply (Water Fittings) Regulations and/or Scottish Water Byelaws . Interpretation given in Part 1: Preliminary of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws Fluid Category 1 Wholesome

Flushing cistern

A cistern provided with valve or device for controlling the discharge of the stored water into a water closet pan or urinal. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Harmonisized standard

A standard established as mentioned in the Directive by the European standards organisation on the basis of a mandate given by the Commission of the European Economic Community and published by the Commission in the Official Journal of the European Communities. Interpretation given in Part 1:

Material change of use

Means a change in the purpose for which, or the circumstances in which, premises are used, such that after that change the premises are used (where previously they were not so used)– (i) as a dwelling; (ii) as an institution; (iii) as a public building; or (iv) for the purposes of the

Maximum level

The highest physical or piezometric level of the fluid reached in any part of the receptacle when operated continuously under fault conditions. Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: terms relating to backflow prevention

Notification

A requirement to provide the water undertaker (water supplier) with advanced notice of a proposal to install a water fitting in connection with any of the operations listed below: 1. The erection of a building or other structure, not being a pond or swimming pool. 2. The extension or alteration of

Overflow pipe

A pipe from a cistern in which water flows only when the water level in the cistern exceeds a predetermined level. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Pressure flushing cistern

A WC flushing device that utilises the pressure of water within the cistern supply pipe to compress air and increase the pressure of water available for flushing a WC pan. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Pressure flushing valve

A self-closing valve supplied with water directly from a supply pipe which when activated will discharge a pre-determined flush volume. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Pressure relief valve

A pressure-activated valve which opens automatically at a specified pressure to discharge fluid. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Primary circuit

An assembly of water fittings in which water circulates between a boiler or other source of heat and a primary heat exchange inside a hot water storage vessel, and includes any space heating system. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish

Regulator

Means– (a) in relation to any water undertakers whose area of appointment is wholly or mainly in Wales and their area of appointment, the National Assembly of Wales; (b) in relation to all other water undertakers and their area of appointment, the Secretary of State; Interpretation given

Regulators' Specification

A specification approved by the Regulators. There are currently three Regulators’ Specifications: the Regulators’ Specification for Water Fittings (test code sheets) the Regulators’ Backflow Specification the Regulators’ WC Performance Specification

Secondary circuit 

An assembly of water fittings in which water circulates in supply pipes or distributing pipes of a hot water storage system. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Secondary system

An assembly of water fittings comprising the cold feed pipe, any hot water storage vessel, water heater and pipework from which hot water is conveyed to all points of draw-off. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Servicing Valve

A valve for shutting off for the purpose of maintenance or service the flow of water in a pipe connected to a water fitting. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Spillover level

The level at which the 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. Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices:

Stopvalve

A valve, other than a servicing valve, used for shutting off the flow of water in a pipe. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Storage cistern

A cistern for storing water for subsequent use, not being a flushing cistern. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Supply pipe

So much of any service pipe as is not vested in the water undertaker for illustration purposes only Interpretation given in Part 1: Preliminary of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Tap gap

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. Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: terms relating to backflow prevention

Temperature relief valve

A valve which opens automatically at a specified temperature to discharge fluid Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Terminal fitting

A water outlet device. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Test code sheets

A series of performance specifications which collectively form the Regulators’ Specification for Water Fittings. To conform to the Regulators’ Specification for Water Fittings a water fittings must satisfy all of the appropriate performance specifications or test code sheets that apply to that

Trap

A pipe fitting, or part of a sanitary appliance, that retains liquid to prevent the passage of foul air. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Type AA – air gap

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 atmosphere. Maximum permissible fluid category against which a Type AA air gap is accepted as adequate backflow

Type AB – Air gap

A non-mechanical backflow prevention arrangement of water fittings complying with Type AA, except that the air gap is the vertical distance from the lowest point of the discharge orifice which discharges into the receptacle, to the critical water level of the rectangular weir overflow. Maximum

Type AC - Air gap

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. Maximum permissible fluid category against which a Type AC air gap is accepted as

Type AD - Air gap

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. Maximum permissible fluid category against which a Type AD air gap is accepted as adequate backflow

Type AF - Air gap

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. Maximum permissible fluid category against which a Type AF air gap is accepted as

Type AG - Air gap

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. Maximum permissible fluid category against which a Type AG air gap is accepted as adequate backflow protection: Backflow by

Type AUK1 - Air gap

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

Type AUK2 - Domestic tap gap

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. Maximum

Type AUK3 - Higher risk tap gap

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. Maximum permissible

Type BA - Backflow prevention device

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. Maximum permissible fluid category

Type CA - Backflow prevention device

A non-verifiable mechanical backflow prevention device which provides disconnection by venting the intermediate pressure zone of the device to the atmosphere when the difference of pressure between the intermediate zone and the upstream zone is not greater than 10% of the upstream pressure.

Type DA - Backflow prevention device

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. Maximum permissible fluid category against which a Type DA device is accepted as

Type DB - Backflow prevention device

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,

Type DC - Pipe interrupter

A non-mechanical backflow prevention device with a permanent unrestricted air inlet, the device being installed so that the flow of water is in a vertical downward direction. Maximum permissible fluid category against which a Type DC arrangement is accepted as adequate backflow protection: Backflow

Type DUK1 - Backflow prevention device

A mechanical backflow prevention device comprising an anti-vacuum valve with a single check valve located upstream. Maximum permissible fluid category against which a Type DUK1 device is accepted as adequate backflow protection: Backflow by back pressure: fluid category 2 Backflow by back

Type EA - Backflow prevention device

A verifiable mechanical backflow prevention device which will permit water to flow from upstream to downstream but not in the reverse direction. Maximum permissible fluid category against which a Type EA device is accepted as adequate backflow protection: Backflow by back pressure: fluid category

Type EB - backflow prevention device

means a non-verifiable mechanical backflow prevention device which will permit water to flow from upstream to downstream but not in the reverse direction. Maximum permissible fluid category against which a Type EB device is accepted as adequate backflow protection: Backflow by back pressure:

Type EC - Backflow prevention device

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. Maximum permissible fluid category against which a Type EC device is accepted as adequate

Type ED - Backflow prevention device

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. Maximum permissible fluid category against which a Type ED device is accepted as adequate backflow

Type HA - Backflow prevention device

A mechanical backflow prevention 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. Maximum permissible fluid category against which a Type HA device is accepted as adequate backflow protection:

Type HC - Backflow prevention devices

"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. Interpretation given in Regulators’ Backflow

Type HUK1- Backflow prevention 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. Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices:

Type LA - Backflow prevention device

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. Maximum permissible fluid category against which a Type LA device is accepted as adequate backflow

Type LB - Backflow prevention device

A mechanical backflow prevention device comprising a Type LA anti-vacuum valve and a single check valve located downstream. Maximum permissible fluid category against which a Type LB device is accepted as adequate backflow protection: Backflow by back pressure: fluid category 2 Backflow by back

Unvented hot water storage vessel

A hot water storage vessel that does not have a vent pipe to the atmosphere. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Upstand - Backflow prevention device

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),

Vent pipe

A pipe open to the atmosphere which exposes the system to atmospheric pressure at its boundary. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Verifiable blackflow prevention device

"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. Interpretation given in

Warning pipe

An overflow pipe whose outlet is located in a position where the discharge can be readily seen. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws

Water Quality Regulators

Various regulatory bodies are responsible for enforcing the legislative requirements to protect the health of consumers and ensure both public supplies meet the requirements of the EU Drinking Water Directive. Some regulators are empowered to take enforcement action against Water Undertakers who

Water trap

Water seal that prevents backflow of odour from the drain Interpretation given in the Regulators’ WC Suite Performance Specification

Water Undertaker

The role of a water undertaker is defined in a number of sections of the Water Industry Act 1991. Water Industry Act 1991

WaterRegsUK

Water Regs UK supports water companies in their role to supply safe, resilient water supplies in the UK. By promoting the Water Fittings Regulations and Byelaws, we protect public health by helping to keep water safe in premises, so it is always safe to drink and never wasted. We work closely with

WC dual flush

Flushing cistern with two modes of operation, one delivering a larger volume than the other in which: the larger (full) flush is not greater than 6 litres: and the reduced smaller flush option is not greater than two-thirds the volume of the larger flush. Interpretation given in the

WC flush volume

Volume of water discharged from the flushing device during a flush cycle. [Note: in the case of devices that require a continuous water supply during flushing (e.g. for outlet seal and/or trap refill) the inflow during flushing forms part of the flush volume.] Interpretation given in the

WC flushing device

Device fitted to a cistern to provide a controlled measured volume(s) of water to a WC for flushing. [Note: a flushing device can be a siphon, drop valve, flap valve or pressurised cistern etc. For the purposes of the WC Specification the flushing device includes the activator (i.e. handle, button,

WC inlet valve

Valve that controls and shuts off the flow of water into a cistern, usually by an arm connected to a float. Interpretation given in the Regulators’ WC Suite Performance Specification

WC suite

WC pan combined with either a flushing cistern with an integral warning pipe connection - or a device deemed to be no less effective device – and an inlet/outlet devices, or a pressure flushing valve, with a WC and flushing device installed as a functioning unit. Interpretation given in the

WC warning level

Level of spillover of a vertically mounted warning pipe connection or the invert of a horizontally mounted warning pipe connection, or the level at which an equally effective (warning) device would operate. Interpretation given in the Regulators’ WC Suite Performance Specification

Wholesomeness

Wholesomeness is defined in section 4 of the Water Supply (Water Quality) Regulations 2010, the prescribed concentrations and values being set out in Schedule 1 of the same legislation. The Water Supply (Water Quality) Regulations 2010

WIAPS

WIAPS is an approved contractors' scheme administered by Water Regs UK on behalf of fourteen water companies.

Workmanlike manner

The installation, connection, alteration, repair or disconnection of a water fitting must be carried out in a workmanlike manner, which is to say the work must be carried out so as to conform:- to an appropriate British Standard, a European technical approval or some other national specification