Page 1 of 9 
 Technical Specification for the  Verification 
and Inspection of Water Meters  S/N CNMV 49  
Rev. 5 
1. This Technical Specification  is enacted pursuant to Paragraph 2, Articles 14 and 16 of 
the Weights and Measures Act.  
2. The date of promulgation, docume nt number, date of enforcement and content of 
amendment are listed as follows:   
Rev. Date of 
Promulgation  Document No.  
(Ching -Piao-Szu-Tsu) Date of 
Enforcement  Content of Amendment  
1 03.18.2003  No. 09240002620  04.01.2003   
2 03.25.2005  No. 09440001090  04.01.2005  Added the dynamic test method 
by referring to CNS 14866  
3 06.25.2008  No. 09740003350  07.01.2008  Revise d as per CNS 14866  
4 12.23.2015  No. 10440018050  07.01 .2016  1. Amending the terms amd 
definition to harmonize with 
the technical specification  for 
type approval.  
2. Adding the minimum water 
volume for verification and 
inspection for vortex water 
meters.  
3. Specifying the maximum 
useable span 8 years for water 
meters with meter designation 
N < 15 or nominal size not 
greater than 40 mm and no 
subsequ ent verification for 
those water meters passed the 
maximum useable span.  
5 12.00.2023  No.1124000000  12.00.2023  Revised with reference to 
OIML R49: 2013  
3. The technical specifications  are laid down by referring to the standards below:  
OIML R49 -1 Water m eters for cold potable water and hot water.  
Part 1: Metrological and technical requirements  （2013） 
OIML R49 -2 Water meters for cold potable water and hot water.  
Part 2: Test methods （2013） 
CNS 13979  V ortex flow meter （08/21/2007） 
 
Date of Promulgation  
 xx xx 2024 Bureau of Standards, Metrology and 
Inspection, Ministry of Economic Affairs  Date of Enforcement  
xx xx 2024 
NO GUARANTEE ON THE TRANSLATION  
In case of discrepancies  between the English translation and Chinese text, the Chinese text shall govern.  
 
Page 2 of 9  
  1. Scope:   
1.1 This technical specification applies to cold potable water meters based on mechanical principle, electrical 
or electronic principle, and mechanical principles incorporating electronic devices, used to measure the 
volume of cold potable water, but not applies to water meters for fire protection.  
1.2 The applicable conditions of the above water meter are as follows:  
1.2.1 The connection method shall be to screw type or flange type, and its inlet and outlet located on both 
sides of the water meter.  
1.2.2 Nominal diameter range is from 13 mm to 300 mm.  
1.2.3 Permanent flow rate is from1.6 m3/h to 1000 m3/h. 
1.2.4 The value of the ratio of permanent flow rate to minimum flow rate is from 50 to 400 (Vortex meter 
is suitabl e from 10 to 40).  
1.2.5 The maximum admissible pressure is equal to or less than 1 MPa.  
 
2. Definitions of Terms  
2.1 Water meter  
Instrument intended to measure continuously, memorize, and display the volume of water passing through 
the measurement transduc er at metering conditions. The indicating device and the water meter shall be 
inseparable  
2.1.1 Volumetric meter  
Device, fitted into a closed conduit, which consists of chambers of known volume and a mechanism 
driven by the flow, whereby these chambers are  successively filled with water and then emptied. By 
counting the number of these volumes passing through the device, the indicating device totals the 
volume flow.  
2.1.2 Velocity meter   
Device, fitted into a closed conduit which consists of a moving elemen t set in motion directly by the 
velocity of the water flow. The movement of the moving element is transmitted  by mechanical or 
other means to the indicating device, which totals the volume flow . 
2.1.3 Woltmann meter  
Device consisting of a helical blade th at rotates about the axis of flow in the meter.  
2.1.4 Single -jet and multi -jet meters  
Devices consisting of a turbine  rotor rotating about the axis perpendicular to the flow of water in the 
meter. The meter is called a single-jet meter if the jet impinges at a single place on the rotor’s 
periphery , and a multi -jet if the jet impinges simultaneously at several points around the periphery of 
the rotor.  
2.1.5 Vortex meters  
Devices comprising a bluff body in the water flow to detect the vortices frequency after  the b luff 
body continuously and integrating an indicator which total the volume flow.  
2.2 Indicating device  
Device displaying the volume flowing.  
2.3 Metrological characteristics  Page 3 of 9  
  2.3.1 Actual volume, Va 
Total volume of water passing through the meter, dis regard ing the time taken. The actual volume is 
calculated from a reference volume as determined by a suitable measurement standard, taking into 
account differences in metering conditions, as appropriate.  
2.3.2 Indicated volume, Vi 
V olume of water indicated  by th e me ter, corresponding to the actual volume.  
2.3.3 Primary indication  
Indication which is subject to legal metrological control.  
2.3.4 Error  
Measured quantity value minus a reference quantity value. The indicated volume is considered as the 
measured quantity value and the actual volume as the reference quantity value. The difference 
between indicated volume and actual volume is referred to as: error.  
In this Technical Specificat ion, the error  (of indication) is expressed as a percentage of the  actual 
volume, and is equal to  
𝑉i−𝑉a
𝑉a×100  % 
 
2.3.5 Maximum permissible error, MPE  
Extreme value of measurement error, with respect to a known reference quantity value, permitted by 
specifications or regulations for a given meter.  
2.4 Operating conditions  
2.4.1 Flow rate, Q 
Q = dV/dt where V is actual volume and t is time taken for this volume to pass through the meter . The 
flow rate is expressed in m3/h. 
2.4.2 Minimum flow rate, Q1 
Lowest flow rate at which the meter is to operate within the maximum permissible errors . 
2.4.3  Transitional flow rate, Q2 
Flow rate between the permanent flow rate and the minimum flow rate that divides the flow rate 
range into two zones, the upper flow rate zone (Q2 ≤ Q ≤ Q4) and the lower flow rate zone (Q1 ≤ Q < 
Q2), each characterized by its own maximum permissible errors.  
2.4.4  Permanent flow rate, Q3 
Highest flow rate within the rated operating conditions at which the meter is to operate within the 
maximum permis sible errors . 
2.4.5  Overload flow rate, Q4 
Highest flow rate at which the meter is to operate for a short period of time within the maximum 
permissible errors, while maintaining its metrological performance when it is subsequently operating 
within  the rate d operating conditions .. 
2.4.6 First element of an indicating device  
Element which , in an indicating device comprising several elements, carries the graduated scale with 
the verification scale interval.  
2.4.7 Verification scale interval  Page 4 of 9  
  Lowest value scale  division of the first element of an indicating device.  
2.4.8  Maximum admissible pressure, MAP  
Maximum internal  pressure that a meter can withstand permanently, within its rated operating 
conditions, without deterioration of its metrological performance.  
2.4.9 Pressure loss, △P 
Pressure loss cased by the presence of a water meter in the pipeline at a given flowrate.  
2.4.10  Nominal diameter, DN  
Alphanumeric designation of size for components of a pipework system, which is used for reference 
purposes.  
2.4.11  Nominal pressure, PN  
Numerical designation  which is a rounded number for reference purposes. All equipment of the same 
nominal size  (DN) and designated by the same PN number  shall have compatible mating dimensions.  
 
3. Metrological requirements  
3.1 Values of Q1, Q2, Q3, and Q4 
3.1.1 The flow rate characteristics of a water meter shall be defined by the values of Q1, Q2, Q3, and Q4. 
3.1.2 The value of Q3, expressed in m3/h, shall be chosen from the following list:  
1.6     2.5      4     6.3      10  
16      25     40     63     100 
160    250    400    630    1000  
3.1.3 The value of the ratio Q3/Q1 shall be chosen from the following  list: (Among them, values ≤ 
40 are only applicable to the vortex flow meter)  
3.1.4 The ratio Q2/Q1 shall be 1.6.  
3.1.5 The ratio Q4/Q3 shall be 1.25.  
3.2 Accuracy class and maximum permissible error  
The water meter shall be designed and manufactured such that its errors  (of indication) do not exceed the 
maximum permissible  errors  (MPEs) as defined in Table 1 under rated operating conditions. The a ccuracy 
class is classified as class 1 or class 2. The manufacturer shall specify the accuracy class.  
Table 1 Accuracy grades and tolerances  
flow rate  MPE  
class 1  class 2  
Q1 ≤ Q  ＜  Q2 ±3 ％ ±5 ％ 
Q2 ≤ Q ≤ Q4 ±1 ％ ±2 ％ 
 
4. Technical requirements  
4.1 A water meter indicating device shall be protected by a transparent window. A cover of a suitable type may 
also be provided as additional protection.  
4.2 The transparent  lid of a wat er meter shall be transparent and clear, and must not be loosened when pressed 
by hand.  The top lid of the water meter shall be opened equal to or more than 120 degrees.  
4.3 Volumetric and velocity multi -jet meters shall be equipped with appropriate strain ers at the lnlet.  Page 5 of 9  
  4.4 The shell of a water meter should not be coated with wax, soluble glass or any other leak proof material; 
the shell of a water meter should be free of sags, crests, scratches or any traces of repair. A position shall 
be reserved for t he lead seal.  
However, the interior and exterior of the shell of a big water meter with a nominal size of not less than 50 
mm may be coated with rustproof paint or powder coating.  
4.5 The appearance of the water meter should comply with the following requi rements:  
4.5.1 The water meter size should be marked on the lid exterior center and the side of water meter, e.g. 13 
mm. 
4.5.2  The direction of flow (→) shall be marked on both sides of the water meter.  
4.5.3  Name or trademark of the manufacturer shall be marked on one side of water meter exterior or on the 
indicating device.  
4.5.4  The serial number should be marked on the edge of meter exterior.  
4.5.5  The indication range (maximum capacity of accumulation) and numbers of meter shall be marked on 
the indicating device.  
4.5.6 The model number  and type approval number shall be marked on the indicating device clearly, but 
this does not apply to those not s ubject to type approval.  
4.5.7 The validity period of verification shall be marked on the edge of the upper shell.  
4.5.8 The installation direction (H) shall be marked on both sides of water meter or on the indicating device 
of water meter . The vortex wate r meters are excluded.  
4.5.9  A water meter shall be clearly and indelibly marked with the information of numerical value of Q3, 
the ratio Q3/Q1, accuracy class, the pressure loss class and nominal pressure. If the meter measures 
reverse flow and the values  of Q3 and the ratios Q3/Q1 are different in the two directions, both values 
of Q3 and Q3/Q1 shall be inscribed.  
4.5.10 The flow profile sensitivity class should be marked in a prominent place.  
4.6 The gear chamber of dry water meters shall be watertight.  
4.7 After verified and sealed, the measurement errors or zero -setting of water meters shall not be able to be 
adjusted by external methods or devices. If the meter is provided with a zero -setting device for special 
purposes, the zeroing position shall be z eroed upon operation, but the totaling device shall not be zeroed.  
 5. Indicating device  
5.1 Functions : 
The indicating device of a water meter shall provide an easily read, reliable, and unambiguous visual 
indication of the indicated volume. The indicating  device shall display the volume either continuously, 
periodically or on demand. The indicating device shall include visual means for testing and verification. 
The indicating device may include additional elements for testing by other methods.  
5.2 Unit of measurement, symbol and its placement:  
 The volume  of water measured shall be expressed in cubic metres. The unit symbol (m3) shall appear on 
the dial or immediately adjacent to the numbered display.  
5.3 Indicating range  
The indicating device shall be able  to record the indicated volume in cubic metres given in Table 2. 
Table 2 Indicating range of a water meter  Page 6 of 9  
  Q3, m3/h Indicating range 
(minimum values) , m3 
Q3≤6.3 9 999  
6.3< Q3≤63 99 999  
63< Q3≤630  999 999  
630<  Q3≤1 000  9 999 999  
5.4 Color coding for i ndicating devices  
(a) Non-electronic digital indicator : The color black should be used to indicate the cubic metres  and its 
multiples . The color red should be used to indicate sub -multiples of a cubic metres . These colors shall 
be applied to either pointer s, indexes, numbers, wheels, discs, dials or to the aperture frames . 
(b) Electronic digital indicator : The color black should be used to indicate the cubic metres  and its 
multiples.  
5.5 Types of indicating device  
5.5.1 Type 1 – Analogue device:  
The indica ted volume is indicated by continuous  movement of  the following (a) and (b)  
(a) one or more pointers moving relative to graduated scales, or  
(b) one or more circular scales or drums each passing an index.  
The value expressed in cubic metres for each scale division shall be of the form 1×10n, where n is a 
positive or negative whole number or zero, thereby establishing a system of consecutive decades. 
Each scale shall either be : 
─graduated in values expressed in cubic metres  
─or accompanied by a multiplication factor (×0.001; ×0.01; ×0.1; ×1; ×10; ×100; ×1 000, etc.)  
Rotational movement of the pointers or circular scales shall be clockwise. Linear movement of 
pointers or scales s hall be left to right. Movement of numbered roller indicators (drums) shall be 
upwards.  
5.5.2 Type 2 – Digital device  
The indicated volume is given by a line of adjacent digits appearing in one or more apertures. The 
advance of a given digit shall be compl eted while the digit of the next immediately lower decade 
changes from 9 to 0. The apparent height of the digits shall be at least 4 mm.  
(a)For non -electronic devices: Movement of numbered roller indicators (drums) shall be upwards. If 
the lowest value dec ade has a continuous movement, the aperture shall be large enough to permit a 
digit to be read unambiguously.  
(b)For electronic devices: Either permanent or non -permanent displays are permitted. For 
non-permanent displays, the volume shall be able to be di splayed at any time for at least 10 s.  
5.5.3 Type 3 – Combination of analogue and digital devices  
The indicated volume is given by a combination of type 1 and type 2 devices and the respective 
requirements of each shall apply.  
5.5.4 Verification scale inte rval 
5.5.4.1 Every indicating device shall provide means for visual, non -ambiguous verification testing. 
The visual verification display may have either a continuous or a discontinuous movement.  Page 7 of 9  
  5.5.4.2  Verification scale interval: The indicator element wi th the smallest decimal number, and its 
smallest decimal scale value is called the verification scale interval. In addition to the visual 
verification display, an indicating device may include provisions for rapid testing by the inclusion 
of complementary elements (e.g. star wheels or discs), providing signals through externally 
attached sensors and convert the recorded data into numerical data.  
5.5.4.3  The value of the verification scale interval expressed in cubic metres shall be of the form: 1 × 
10n, 2 × 10n or 5 × 10n, where n is a positive or negative whole number, or zero. For analogue and 
digital indicating devices with continuous movement of the first element, the verification scale 
may be formed from the division into 2, 5 or 10 equal parts of the i nterval between two 
consecutive digits of the first element. Numbering shall not be applied to these divisions.  
5.5.4.4  Form of the verification scale:  
(a) On indicating devices with continuous movement of the first element, the apparent scale 
spacing shal l be not less than 1 mm and not more than 5 mm.  
(b) On indicating devices with non -continuous movement of the first element, the verification 
scale interval is the interval between two consecutive digits or incremental movements of the 
first element.  
5.5.5  The minimum verification scale of the indicating device shall meet the requirements in Table 3.  
Table 3 Minimum subdivisions value  
 
 
 
 
(a) If the mini mum verification scale is continuous, an allowance shall be made for a maximum 
error in each reading of not more than half the verification scale interval.  
(b) If the mi nimum verification scale is discontinuous, an allowance shall be made for a 
maximum err or in each reading of not more than one digit of the verification scale.  
 
6. Verification, Inspection and Maximum P ermissible  Errors  
6.1 Verification and inspection equipment: A certificate is required to identify the traceability and uncertainty 
of the sy stem of the verification equipment.  
6.1.1 Necessary equipment:  
(a)It can be the volume method  or the weighing method. The expanded uncertainty of the equipment used 
shall not exceed one -third  of the  MPE , and the coverage factor of the estimated uncertainty  is k=2. 
(b) The accuracy of the measurement error of the minimum division value should be less than 1/500 of 
the verified and inspected water volume, and its capacity range should be set according to the Q3 value 
and Q3/Q1 ratio of the verified and inspec ted water meter.  
6.1.2  Pressure test device: The device shall be able to pressurize up to more than 2 MPa for pressure test 
use. 
6.1.3  Timer device: The device shall equip with minimum scale value less than 0.2 seconds . Accuracy  continuous  discontinuous,  
Class 1  1.5Q10.25％ 1.5Q 10.125％ 
Class 2  1.5Q 10.5％ 1.5Q 10.25％ Page 8 of 9  
  6.2 Static pressure test : Every wat er meter shall be able to endure pressure test up to 1.6 times the maximum 
admissible pressure applied for 1 min without leakage or damage. For a water meter with a dry indicating 
device, water should not be immersed in the upper gear chamber and the indic ating device.  
6.3 Meters are tested either individually or in groups. In the latter case, the straight lengths between the meters 
shall be enough. The presence of any meter in the test rig shall not contribute significantly to the test error 
of any other m eter. During the tests, the gauge pressure at the outlet of each water meter shall be at least 
0.03 MPa (0.3 bar).  
6.3.1 Testing method with readings taken with the flow passing the meter still  
(1) After the water meter is installed, water shall be put in to vent the air out from the water meter and 
piping system, then setting verifying flow rate by adjusting the outlet cock (valve).  
(2) Prior to putting in water for verification, the meter’s indicating value and its standard equipment’s 
indicating value sh all be recorded.  
(3) After the water volume for verification has passed, the outlet cock (valve) of the system shall be 
closed so as to avoid backflow, then closing the inlet cock immediately, record the meter’s indicating 
value and the necessary equipment ’s value after the water flow completely stops.  
6.3.2  Tests with readings taken under stable flow conditions and diversion of flow  
(1) After completing the installation of the water meter, water shall be put in to vent the air out from the 
water meter and piping system, then setting verifying flow rate by adjusting the outlet cock (valve).  
(2) Prior to putting in water for verification, the meter’s indicating value and the necessary equipment’s 
indicating value shall be recorded.  
(3) The test procedure is c arried out after the flow reaches steady. The flow is diverted into a calibrated 
vessel at the beginning of the procedure and diverted it away at the end. The meter is read while the 
flow passing. The reading of the meter is synchronized with the movement of the flow diverting. 
The volume collected in the vessel is the volume passed. The uncertainty of the collected volume 
may be considered negligible if the times deviation of each flow diverting is less than 5% and the 
diverting time is less than 1/50 of t he total time of the procedure.  
6.4 Flow -rate and minimum passed water volume for verification and inspection   
6.4.1  Verification flow point Q 
(1) Q1≤ Q≤ 1.1 Q1。 
(2) Q2≤ Q≤ 1.1 Q2。 
(3) 0.9 Q3≤ Q≤ Q3。 
Among them, 1 % of the water  meters applied for verifica tion shall be sampled and  
tested for error at  the verification flow point Q1≤ Q≤ 1.1 Q1, and at least 1 meter  shall be tested . 
6.4.2  Tests method  with readings taken with the flow passing the meter still   
The minimum water volume for verification and insp ection = The minimum meter scale value 
multiplied by 200, which  shall not be less than the volume accumulated from  2.5 minutes of flow . 
6.4.3  Tests with readings taken under stable flow conditions and diversion of flow  
The relative variation  of the flow –rate for verification shall be within the range of 5%.  
The minimum water volume for verification and inspection = The minimum meter scale value 
multiplied by 200, which shall not be less than the volume accumulated from 1 minute  of flow  Page 9 of 9  
  6.5 Error are specifi ed in Table 1.  
6.6 The maximum permissible  errors for inspection of water meters are twice the maximum permissible  errors 
for verification.  
6.7 Valid period of verification  
The valid period of verification for water meters is eight years , starting from the  date of the very beginning 
of next month of obtaining the verification certification.  
6.8 Maximum useable span   
The maximum useable span for meters  with Q3≤16 or nominal size not greater than 40 mm is 8 years after 
passing initial verification; however, for the maximum useable span for meters with Q3＞16 o r nominal 
size greater than 40 mm is 10 years after passing initial verification. To apply for subsequent  verification 
for meter that over its maximum useable span is not allowed.  
 
7. Verification marks   
7.1 The verification marks shall be pressed with lead sealing between the metal wire and the opening of the 
outer case lead sealed through the lock. Also, th e words “valid period of verification year month” shall be 
printed on the edge of the upper outer case.  
7.2 For a large meter with the designation of Q3＞16 or a nominal size greater than 40 mm passing the 
subsequent verification, the maximum useable span  shall be additionally marked on the edge of the meter’s 
upper outer case.  
 
8. Implementation date ：This specification will come into effect from now on. H owever, if the correction 
according to the fourth edition of the  technical specification for type approval of water meters has not been 
completed before December 31, 20 27, as notified by the dedicated weights and measures authority, the 
following provision s shall apply:  
(1)The specification before the amendment is implemented  will apply before December 31, 20 27. 
(2) The dedicated weights and measures authority has received the application for amendment to the fourth 
edition of the technical specification fo r type approval of water meters before December 31, 20 27. If the 
review is completed after that date, the specification before the implementation of the amendment will 
apply before the review is completed.  
  