Guidance

MCERTS for water flowmeters Part 2: performance standards and test procedures for closed conduit instruments

Updated 24 August 2026

Applies to England

Introduction

The Environment Agency set up the Monitoring Certification Scheme (MCERTS) to provide guidance on the standards you must meet to monitor emissions that affect the environment. The scheme is based on international standards. It provides for the product certification of instruments, the competency certification of personnel and the accreditation of laboratories.

This guidance is for:

• manufacturers of water flowmeters for use on closed conduits and partially filled pipes who need to know what standards to meet to be able to use their equipment for regulatory purposes in England and Wales
• test organisations who carry out testing of the equipment on behalf of manufacturers to see if it meets the required standard

We designed MCERTS to support the measurement requirements specified in environmental permits by making sure that equipment used to derive monitoring data is fit for purpose.

Closed conduit continuous water flowmeters

A continuous water flowmeter is an instrument that measures the flow-rate or totalised volume of water passing along an open channel or conduit. It computes such quantities from measurements of one or more properties which have a defined relationship with the flow-rate.

Closed conduit continuous water flowmeters are used to measure the flow of water in closed pressurised pipes and partially filled pipes that may become surcharged and behave as a pressurised pipe. They are referred to as closed conduit instruments (CCI). They are used to measure the flow of treated discharges from wastewater treatment works, industrial processes, untreated wastewater and receiving waters.

Continuous water flowmeters that can only operate in partially filled pipes with free surface conditions shall be tested in accordance with MCERTS performance standard for water flowmeters: part 1 – open channel instruments.

Certification body

We have appointed CSA Group Testing UK Ltd (CSA Group) as the certification body to operate MCERTS on our behalf.

CSA Group Testing UK Ltd complies with EN ISO/IEC 17065 Conformity assessment – Requirements for bodies certifying products, processes and services.

If you have any questions about the certification process or would like more information on how to make an application, please contact CSA Group Testing UK Ltd.

More information about MCERTS is available in the Monitoring emissions to air, land and water collection on GOV.UK.

If you have any general questions about MCERTS, please contact the Environment Agency.

Certification committee

The certification body appoints a certification committee to make certification decisions. The committee is made up of appropriately independent, competent person or group.

MCERTS certification

Product certification comprises of 2 phases. These are:

• laboratory and field testing – used to determine performance characteristics, where such testing requires a highly controlled environment (field testing is carried out on processes representative of the intended industrial sectors and applications)
• surveillance – initial and continuing which comprises an audit of the manufacturing process (to confirm that the manufacturer has provisions to ensure manufacturing reproducibility and to control any design changes to ensure that they do not degrade performance below the MCERTS requirements)

MCERTS continuous flowmeter scheme

MCERTS for continuous water flowmeters provides the product certification of CCI and open channel instruments. Information about open channel instruments is available at MCERTS performance standard for water flowmeters part 1: open channel instruments.

Water flowmeters may be certified against either one or both parts of this standard.

1. Summary

In this section we introduce the scheme.

1.1 Background

1.1.1 The European standard which forms the technical basis of the MCERTS requirements for CCIs is ‘EN 17694-2:2023 – Hydrometry – Minimum performance requirements and test procedures for water monitoring equipment – Devices for the determination of flow – Part 2: Closed conduit instrumentation’

1.1.2 The requirements in this document and EN 17694-2 are intended to be technology transparent and allow the certification of any technical solution that meets the requirements.

1.1.3 Definitions of terms used in this document are provided in section 3 of EN 17694-2. Additional terms are provided in this document.

1.1.4 The Environment Agency requires operators of regulated processes to use MCERTS certified continuous water flowmeters.

1.1.5 It is the responsibility of the user to make sure that the selection, installation and operation of a CCI is appropriate to the application.

1.1.6 EN 17694-2 specifies general requirements, minimum performance requirements and test procedures applicable to CCIs used to determine either volumetric flow-rate, total volume or both. It covers instrument technologies intended to be used in closed pressurised pipes and those that operate in partially filled pipes that experience surcharge conditions.

1.1.7 Performance tests for the product certification of a CCI against these MCERTS requirements shall be carried out in accordance with the procedures specified in this document and EN 17694-2.

2. Scope of the MCERTS scheme

MCERTS certified CCIs can be required for use on a range of sites including:

• processes under the Environmental Permitting Regulations
• consented discharges for processes regulated through provisions of the Water Resources Act, 1991
• sites under the Urban Wastewater Treatment Regulations (UWWTR)
• sites under the Radioactive Substances Regulations
• sites under other relevant directives, for example, the Water Framework Directive
• other monitoring of the aquatic environment

Information on flow and event duration monitoring installations is available in Minimum requirements for self-monitoring of flow: MCERTS performance standard.

3. General requirements

This section describes general requirements for the identification, design and operation of CCIs, and information required in manufacturers’ documentation.

The general requirements shall be assessed by inspection or the manufacturer’s statement.

3.1 Requirements for CCIs

3.1.1 CCIs shall meet the general requirements specified in EN 17694-2 (section 6.1).

3.1.2 MCERTS certified CCIs shall have a unique designation that clearly identifies the CCI as a MCERTS certified model. To enable identification of an MCERTS certified CCI, reference may also need to be made to versions of software and firmware installed in the CCI.

3.1.3 Any additional equipment required for the CCI to operate continuously on site within the requirements of this standard shall be available from the manufacturer. This shall include but not be limited to, upstream strainers or filters, sunshades, batteries and secondary enclosures.

3.1.4 Attaching an ancillary device to the CCI shall not reduce the rated operating conditions for any environmental parameter.

An ancillary device is any additional equipment that may be required for operation of the CCI but which does not normally form part of the CCI package. Examples include external data loggers or telemetry equipment, power conditioning devices, lightning protection, external pumps or compressors required for automatic cleaning systems.

3.1.5 An electronic CCI shall have a means of automatically communicating faults to a remote system.

3.1.6 A CCI intended for regulatory reporting shall have a means for preventing unauthorised resetting of the total recorded volume.

3.2 Requirements for associated documentation

3.2.1 Manufacturers’ associated documentation shall meet the requirements specified in EN 17694-2 (section 6.2).

3.2.2 The manufacturer’s documentation shall include a statement on the CCI’s maximum and minimum range for all measurement parameters.

3.2.3 For CCIs with non-contact velocity sensors, the manufacturer shall provide guidance on the water surface conditions required to maintain performance within the requirements of this standard.

4. Performance requirements

This section describes the performance requirements for CCIs.

4.1 Expression of performance requirements

Performance requirements for CCIs shall be expressed as specified in EN 17694-2 (section 7.1).

4.2 Performance requirements for CCIs

The performance requirements for CCIs shall be as specified in EN 17694-2 (section 7.2). However, Table 1 of this document shall be used in place of Table 2 of EN 17694-2, to reflect the performance requirements and classes of the MCERTS scheme.

MCERTS class 1 requirements for CCIs are equivalent to the performance requirements specified in EN 17694-2.

Table 1: MCERTS CCI performance requirements by class

Determinand	Symbol	MCERTS clause	MCERTS – class 1 % error	MCERTS – class 2 % error	MCERTS – class 3 % error
Bias	b	6.3.2	±1.5	±4	±6.5
Lower limit value for mean error (see note 1)	N/A	6.3.2	±5	±10	±10
Repeatability	SR	6.3.2	1	2	4
Supply voltage	XV	6.3.3	0.5	1	2
Output impedance	XO	6.3.4	0.5	1	2
Water temperature	XFT	6.3.5	0.5	1	2
Ambient air temperature	XT	6.3.6	0.5	1	2
Relative humidity	XRH	6.3.6	0.5	1	2
Sensor location	XSL	6.3.7	0.5	1	2
Stray currents	XSC	6.3.8	0.5	1	2
Combined performance (see note 2)	UC	N/A	2	5	8
Maximum response time (see note 3)	N/A	6.3.15	30 seconds	30 seconds	30 seconds
Warm up	N/A	6.2	To be reported	To be reported	To be reported

Note 1: The lower limit value for mean error is only applicable from the minimum value to the minimum value plus 10 % of the measurement range.

Note 2: The combined performance requirement is less than the sum of the specified individual performance values combined in quadrature. This allows for some differences in performance of CCIs with respect to the individual requirements within an overall combined performance requirement.

Note 3: The response time of a CCI will be assessed over a variation in flow-rate of at least 20 % of the measurement range.

4.3 Data retention

CCIs shall meet the data retention requirements specified in EN 17694-2 (section 7.3).

4.4 Environmental requirements

CCIs shall meet the environmental requirements specified in accordance with EN 17694-2 (section 7.4).

4.5 Water temperature requirements

CCIs shall meet the water temperature requirements specified in accordance with EN 17694-2 (section 7.5).

4.6 Installation influences

CCIs shall meet the installation influences requirements specified in accordance with EN 17694-2 (section 7.6).

4.7 Field test requirements

CCIs shall meet the field test requirements specified in accordance with EN 17694-2 (section 7.7).

5. Provisions for test organisations

This section describes the provisions for organisations testing CCIs.

5.1 General requirements for testing

All testing of CCIs for MCERTS shall be conducted in line with the requirements specified in EN 17694-2 (section 8.1).

The results of other tests may be acceptable to the certification body, if they are shown to be equivalent to MCERTS and carried out independently. Manufacturers’ own test data may also be considered, if it also meets the MCERTS requirements for testing and data quality.

5.2 Laboratory test conditions

CCIs shall be tested at the reference conditions and test point values specified in EN 17694-2 (section 8.2).

5.3 Reporting

Test results shall be reported as specified in EN 17694-2 (section 8.3).

6. Laboratory test procedures

This section describes the laboratory test procedures.

6.1 Establishing a test plan

Before testing is started, a test plan, which meets the requirements of EN 17694-2 (section 9.1), shall be agreed with the MCERTS certification committee.

6.2 Verification by inspection

6.2.1 The CCI shall be inspected to verify conformity with the requirements in EN 17694-2 (section 9.2).

6.2.2 The CCI shall be inspected to verify conformity with the additional general requirements listed in this document.

6.2.3 The CCI’s associated documentation shall be inspected to verify that the general requirements listed in this document are fulfilled.

6.3 Performance tests

Performance tests should be carried out following the agreed test plan.

6.3.1 Loss of power for electronic CCIs

Determine the influence of loss of power on the performance of the CCI in accordance with EN 17694-2 (section 9.3.1).

6.3.2 Bias (mean error) and repeatability

Determine the bias and repeatability of the CCI in accordance with EN 17694-2 (section 9.3.2).

6.3.3 Supply voltage

Determine the influence of changes in supply voltage on the CCI in accordance with EN 17694-2 (section 9.3.3).

6.3.4 Output impedance

Determine the influence of changes in output impedance on the CCI in accordance with EN 17694-2 (section 9.3.4).

The output is a displayed reading, or a digital or analogue electrical signal, generated by an instrument in response to a measurand.

6.3.5 Water temperature

Determine the influence of changes in water temperature on the CCI in accordance with EN 17694-2 (section 9.3.5).

6.3.6 Ambient air temperature and relative humidity

Determine the influence of changes in ambient temperature and relative humidity on the CCI in accordance with EN 17694-2 (section 9.3.6).

6.3.7 Sensor location

For non-contact velocity sensors used in partially filled pipes only, determine the influence of changes in the sensor location on the CCI in accordance with EN 17694-2 (section 9.3.7).

6.3.8 Presence of stray currents

Determine the effect of stray currents on the CCI in accordance with EN 17694-2 (section 9.3.8).

6.3.9 Bi-directional flow

Determine the effect of bi-directional flow on the CCI in accordance with EN 17694-2 (section 9.3.9).

6.3.10 Flow reversal

Determine the effect of flow reversal on the CCI in accordance with EN 17694-2 (section 9.3.10).

6.3.11 Ancillary devices

Determine the effect of ancillary devices on the CCI in accordance with EN 17694-2 (section 9.3.11).

6.3.12 Effect of conduit material

Determine the effect of the conduit material on the CCI in accordance with EN 17694-2 (section 9.3.12).

6.3.13 Effect of conduit size

Determine the effect of the conduit size on the CCI in accordance with EN 17694-2 (section 9.3.13).

6.3.14 Fill level

Determine the effect of the conduit fill level on the CCI in accordance with EN 17694-2 (section 9.3.14).

6.3.15 Response time

Determine the response time of the CCI in accordance with EN 17694-2 (section 9.3.15).

6.3.16 Combined performance requirement

Upon completion of the laboratory testing, calculate the combined performance characteristic using the procedure specified in EN 17694-2 (Annex A, section A.5).

7. Field test procedures

This section describes the field test procedures.

7.1 Objective of field test

The objectives of the field test are specified in EN 17694-2 (section 10.1).

7.2 Field test plan

7.2.1 The requirements of the field test plan are specified in EN 17694-2 (section 10.2).

7.2.2 The certification body can provide advice on different practical approaches to implementing the field test plan. A questionnaire is available from the certification body to assist in collating the information required to establish whether data from an existing installation would be acceptable for product certification.

7.2.3 The test plan detailing the proposed field trial shall be submitted to the certification body for consideration by the certification committee. The decision of the certification committee on matters related to the test plan and data is final.

7.3 Field test requirements

7.3.1 The requirements of the field test are specified in EN 17694-2 (section 10.3).

7.3.2 Data obtained when conditions are outside the rated operating conditions can be reported to demonstrate performance in excess of the MCERTS requirements.

7.4 Error under field test conditions

The error of the CCI under test shall be determined as specified in EN 17694-2 (section 10.4).

The error is the difference between the value given by the CCI and the reference quantity value.

7.5 Up-time

The up-time of the CCI under test shall be determined as specified in EN 17694-2 (section 10.5).

7.6 Maintenance

The details of any maintenance shall be recorded as specified in EN 17694-2 (section 10.6).

The certification body shall be contacted for approval if any major components are replaced during the field trial.

7.7 Reporting of the field test

The field test shall be reported as part of the report specified in EN 17694-2 (section 8.3).

8. Evaluation of test data

Test data shall be evaluated according to the procedures specified in EN 17694-2 Annex A.

9. Reference methods

Guidance on reference methods applicable to this document are available in EN 17694-2 Annex B.

10. Reference uncertainty and error calculation

Uncertainty is the parameter associated with the result of a measurement that characterises the dispersion of the values that could reasonably be attributed to the measurand.

Guidance on reference uncertainty and error calculation is specified in EN 17694-2 Annex C.

11. MCERTS product certification

Manufacturers seeking product certification should contact the certification body, who will advise on specific requirements for the water flowmeter under consideration.

11.1 Certification process

A CCI shall be a fully functioning water flow monitoring system. CCIs can be supplied with several options, for example different sizes, or with remote or integrated transmitters of sensor signals, or where more than one sensor or sensor configuration can be used to cover different ranges. The certification committee shall review how different options may affect performance and decide on the tests that are required for each option.

When selecting the options to be tested, consideration should be given to the specification of the CCI likely to be used for each of the identified applications. For additional sensors, sensor configurations or other options, it may be possible to extend certification by carrying out a subset of the full test programme. Where options are likely to have a significant effect on the performance of the CCI selected, additional tests may be required. Similarly, where different transmitters having different facilities are used with a single sensor, one complete CCI shall undergo the full conformity tests. For additional transmitters, it may be possible to extend certification by carrying out a subset of the full test programme.

11.2 Certification body and committee

The role of the certification body is to assess and certify compliance with the MCERTS standard for defined applications and or conditions.

In performing this role, the certification body shall consider the relevance of the procedures defined in the MCERTS requirements for the product to be certified.

Following approval from the certification committee, an evaluation is undertaken by an independent reviewer associated with the certification body, who makes a final certification decision.

On request, the certification body shall provide the Environment Agency with the rationale for any certification decision.

11.3 Certification range

The CCI will be certified over the measurement range for which it is tested. If a manufacturer wishes to demonstrate performance over one or more supplementary ranges, some additional testing will be required over those ranges. This additional testing shall at least include evaluations of bias and repeatability.

11.4 Testing

Manufacturers may commission testing from any organisation, provided that the requirements for testing organisations can be met. Manufacturers’ own test data may also be considered but should be assessed to demonstrate that it conforms to the requirements for test laboratories. This applies to both laboratory and field tests.

The results of previous performance tests may be acceptable to the certification body if they are equivalent to MCERTS requirements and were carried out independently. Any subsequent changes to the CCI shall be demonstrably not significant.

Certain tests may present practical difficulties for certain types of CCIs. In such cases, manufacturers should inform the certification body, so that the most appropriate course of action can be determined.

11.5 Auditing and surveillance

An audit of the manufacturing process shall be conducted by the certification body. This is to confirm that the manufacturer has provisions to make sure of manufacturing reproducibility and to control any design changes that may affect product performance.

Subsequent surveillance audits are normally conducted annually until sufficient evidence of a well-proven, robust system has been collected. Once this has been established the certification body may extend the interval between audits or require submission of specific audit data for review off site.

11.6 Certificate validity

MCERTS certificates are valid for 5 years. After this time, the certification is reviewed and any necessary retesting will be identified to maintain the product certification. Modifications to the CCI shall be considered as part of this process.

Assessment for recertification shall be carried out against the MCERTS performance standard current at the time of recertification.

11.7 Modifications to certified CCIs

Modifications and design changes include changes to all components of the flow or level measurement system, including software and firmware.

Any spares or replacement parts for certified CCI must meet the same performance standards as the original parts. Manufacturers may be required to provide evidence that the replacement parts meet the required performance standards of the original equipment as specified by the manufacturer of the CCI.

Modifications to certified CCI are allowable so long as manufacturers can demonstrate that these design changes do not degrade the performance of the CCI below the MCERTS requirements.

Manufacturers shall keep detailed records and drawings of all design changes to CCI, and have provisions for design verification, inspection and testing to make sure that the CCIs still meet the required performance standards.

To meet the requirements of product certification, the certification body shall conduct audits of the design changes to CCI. Manufacturers shall notify the certification body of any modifications to equipment that may have a significant effect on CCI performance.

Design modifications or extensions to the range of application of a CCI may require renewed testing. The extent of this renewed testing will depend upon the nature of the modifications to the CCI.

If there is evidence that a modification has only limited effects on the performance of the CCI, then it would not be necessary to retest a CCI completely. In such cases, only a supplementary test would be required to the applicable MCERTS performance standards.

In the case of modifications to software, particularly in measuring instruments, detailed documentation shall be presented to the certification body indicating the nature of the modification as well as resultant effects on operation and functionality. The certification body will then decide if further testing is required.