Water Meters (Domestic Type)
1994 Edition

According to IS 779:1994, acceptable materials for domestic water meters must possess sufficient mechanical strength and stability, exhibit resistance against internal and typical external corrosion, and be non-toxic to ensure water safety. Corrosion-resistant metals or suitably treated surfaces are recommended, and the use of dissimilar metals in contact under water is discouraged to prevent galvanic corrosion. Dial components may be fabricated from plastics such as high impact polystyrene, acrylic, or acetal co-polymer. Notably, ferrous metals for type B water meters have been phased out as per Amendment No.3. These criteria ensure durability, safety, and compliance with IS 779 and related standards.

IS 779 categorizes domestic water meters into three metrological classes influenced by ISO 4064 (Part 1) and the EEC Directive: Class A denotes high-accuracy meters with stringent requirements; Class B represents moderate accuracy with more relaxed tolerances; Class O (ordinary) serves as a transitional class for existing industry needs but is scheduled for withdrawal three years post-publication. Accuracy limits specify a ±5% error in the lower flow range (Qmin to Qt) and typically ±2% in the upper flow region (Qt to Qmax) as per IS 6784. The classification hinges on maximum verification scale intervals and metrological performance, ensuring reliability and precision in domestic water measurement.

To achieve precise measurements and long-lasting performance in accordance with IS 779, meters should be installed following specific conditions: Inferential meters must be mounted horizontally with the dial facing upward; the flow direction marked on the meter must be observed; the pipeline should be thoroughly flushed prior to installation; upstream filters or dirt boxes are essential to prevent particulate ingress, and the meter's integral strainer must remain intact. Installation sites should avoid exposure to water hammer effects, and air release valves are recommended in intermittent supply systems to prevent air entrapment. Additionally, verifying seals, serial numbers, and test certificates before installation is crucial. These practices collectively ensure measurement accuracy and meter longevity.

IS 779 mandates a comprehensive quality assurance testing protocol including submission of three identical meters per size and class along with detailed manufacturer specifications to an accredited testing facility. Type tests encompass pressure tightness verification via hydrostatic testing and flow performance evaluations measuring pressure loss, metering accuracy, minimum starting flow, and temperature resistance. Meters must undergo preconditioning by running water at nominal flow for two hours before testing. These procedures, guided by clauses 12.1 to 12.5 and IS 6784, ensure meters meet the required performance and durability standards.

IS 779 specifies that pressure losses in domestic water meters must not exceed 0.025 MPa at the nominal flow rate (Qn) and 0.1 MPa at the maximum flow rate (Qmax), where Qmax is typically double Qn. Flow rate parameters define minimum starting flow (Qmis), transitional flow (Qtr), and maximum flow (Qmax) values dependent on meter size and class. For example, a 15 mm meter ranges from 30 to 90 l/h minimum starting flow across classes B to O, with transitional flows between 120 to 180 l/h and a maximum flow of 3 kL/h. Meters undergo flow tests to verify these criteria after conditioning. These standards ensure efficient operation within designated pressure and flow limits.