According to the laws in most countries (including Bosnia and Herzegovina) Water Supply Companies shall perform calibration of water meters up to 40 mm diameter   in a maximum of five years, and watermeters larger than 40 mm in a maximum of three years.

Utility have  interest  that calibration is done as soon as possible because water meters as well as any device that uses some kind of bearings during the time caused an increase in resistance and decrease in the number of revolutions, so the meter shows less consumption of real, and what is the loss for water supply company.

Waterworks which have not performed calibration or replacement of water meters for a long time , at the time when they do usually have  frequent protests of citizens, who are convinced that their new watermeter was not correct, "because the old one showed much lower consumption." 

Water meters "are"  cashbox for waterworks, and according to that, particular attention should be paid to the big meters (with diameter bigger than 40 mm), because them size is proportionally match the size losses .In the  world there are two recognized methods for Water meters calibration :

• Calibration in the calibration station or
• Test in the Place calibration

Fulfillment of conditions for testing of large water meters in the Place

Test in the place  calibrating method for large water meter (diameter greater than 40 mm) is regulated in most countries in the world. Unfortunately, when it comes to the south-eastern European countries  law does not approve this method, and  all the water meters regardless of size must be calibrated in calibration station.

Large size water meters are installed on pipe using a flange and bolts, and their removal is not easy. Besides that the water meter's weight  is between 10 and 120 kg depending on the manufacturer and the diameter of the water meter, which is an additional problem for booting from the chamber and transport to calibration station.

The law stipulates that a large water meters must be calibrated within a maximum of three years. If the waterworks in this term did not calibrate, it is considered that the meter was not correct and according to that, waterworks can not  billing for consumption measured with that meter

A well-informed consumers generally don't have objections if the waterworks didn't performe calibration of water meters during proscribed time  from the simple reason that the readings which will be perform far less than the real consumption that the consumer achieved.

The practice of waterworks in  United States is that the calibration of large water meters shall provide continuously regardless what the  legal regulations also stipulate that the deadline for the calibration of large water meters is 3 years. The theory that I have heard from Mr. Haris Saidela, (General manager in one waterworks in Iowa state -USA) is that water meters are cashbox for the waterworks , and  a according that large water meter register, big money. Based on that theory  water utilities in the U.S. have a team who are constantly on the field and performe  control or calibration action  on the big water meters, and the time between two calibration amounts less than one year.

In countries where, according to the current legislation, calibration of water meters on the site still can not be performed, however can be tested (control accuracy of water meters), and only those meters for which this method finds thatare no  accurate can be removed and sent to calibration station.

In most western countries connector has exactly look like connector presented on  the right picture. By-Pass is usually temporary, and sometimes permanent, only serves to the consumer not left without water supply during the testing time . Also be seen that the filter is  in front of the consumer meter integral part of the connector's structure .

Large water meter testing in place is much simpler, cheaper and much more accurate than their bringing to the workshop for testing.

1. Check the installation and verify the identification number of the water meter, its size etc.

2. Easily open the by-pass (if there is one);

3. Isolate customer water meter by closing both valves;

4. Clean the filter/strainer;

5. Ensure that the outlet/downstream valve is tightly closed in order to avoid leaking during testing;

6. Connect the pipe to the test fitting;

7. Open the front valve;

8. Let a small stream of water into the pipe in order to remove all the remainings;

9. Connect the pipe to the portable test water meter;

10. Connect the outlet hose to the adequate location forBefore initiating the testing, ensure that both water meters are full of water and under positive pressure;

11. Initiate testing at lowestThe flow is controlled by manipulating the ball valve at the outlet side of the test water meter;

12. Do an additional test with increasedMaximum flow should not exceed  20?30 % of the total capacity or the customer water meter rating;

13. Record pressure. The pressure downstream of the customer water meter should not drop below 1,5 atm;

14. Record flow and time for each test;

15. Precise flow (l/s) does not matter; the goal of testing is to compare the volume (liters) of water;

16. Calculate the accuracy of customer water meter after each test;

17. Depending on the type of water meter, if need be, setting and repairs could be done on site;

18. After the adjustment of settings and repairs, retest the water meter in order to determine whether its accuracy is now acceptable;

19. Disconnect the mobile water meter and return everything back to normal;

20. Close and secure the by-pass.

Remarks:

Test water meter does not have to be an expensive type of water meter.  A good water meter, regularly calibrated shall serve the purpose.

Test water meter does not have to be of the same size as the customer one.  For instance, a 50 mm test water meter would be adequate for determining the accuracy of a 100 mm or even 150 mm customer water meter.

 If the customer water meter indicates any type of deviation, it is being demounted and sent to the calibration workshop, and a new accurate water meter is installed in its place. 

For easier processing of test results is useful to prepare a table in MS Excel or a similar software. One such tool can be download here