Water Meter Accuracy Guide

Water meter accuracy is not a widely understood concept outside of professional plumbers, water utility engineers, and industry experts. Water meter accuracy is classified according to flow rate precision (Class A, Class B, Class C, & Class D). That means, different types of water meters have different degrees of error at different rates of consumption. This has potentially costly consequences if incorrectly rated water meters are installed.

How Accurate Are Water Meters?

Water meter accuracy is vitally important. To understand how accurate water meters are, one must examine the classification system – ISO 4064-1 (2014). This standard defines 4 vitally important metrics: Qn, Qmax, Qmin, and Qt.

Qn (Nominal Flow Rate) is defined as the designated flow rate of the water meter.
Qmax (Maximum Flow Rate) is defined as the highest flow rate at which the meter accuracy will be within the maximum permitted error (±5%).
Qmin (Minimum Flow Rate) is defined as the lowest flow rate at which the meter will be within the maximum permitted error.
Qt (Transitional Flow Rate) is defined as the flow rate at which the maximum permitted error of the meter changes from ±5% to ±2%.

Water Meter Accuracy Classification

Nominal Diameter	Qn (m3/hr)	Qmax (m3/hr)	Class A		Class B		Class C		Class D
Nominal Diameter	Qn (m3/hr)	Qmax (m3/hr)	Qmin (litres/hr)	Qt (litres/hr)	Qmin (litres/hr)	Qt (litres/hr)	Qmin (litres/hr)	Qt (litres/hr)	Qmin (litres/hr)	Qt (litres/hr)
15(½)	1.0	2.0	–	–	–	–	–	–	7.5	11.5
15(½)	1.5	3.0	60	150	30	120	15	22.5	11.25	17.25
20(¾)	2.5	5.0	100	250	50	200	25	37.5	18.75	28.75
25(1)	3.5	7	140	350	70	280	35	52.5	26.25	40.25
25(1)	6.0	12	240	600	120	480	60	90	–	–
32(1½)	6.0	12	240	600	120	480	60	90	–	–
40(1½)	10	20	400	1000	200	800	100	150	–	–

Water Meter Accuracy in Practical Application

Ironically, water meter accuracy may seem a dry subject but upon examination of practical applications, one can see that it’s quite interesting:

On the 18th of August 2021, WUS Experts installed a water meter to monitor the catering kitchen at a Faircape Life luxury retirement village (Heritage Manor). These secure luxury estates feature fine catering cooked and plated to perfection at the on-site kitchen. Professional kitchens like this can serve in excess of 500 meals a day! This involves large volumes of water for both preparation and sanitation.

Accurate Water Meter Benefits: Heritage Manor kitchen water consumption profile revealed continuous consumption running throughout the night.

The installation of this water meter in the kitchen allowed for the appropriate level of accuracy to measure a previously undetected stream of continuous water consumption. As the graph above displays, the kitchen was consuming approximately 100 litres per hour every hour at night.

Using advanced features of READy, WUS Experts reduced the measurement interval from 1 hour to 5 minutes – providing extreme precision and revealing a more detailed consumption profile. WUS Experts then used a process of elimination to isolate the source of consumption. Geyser valves were examined and toilet cisterns were checked but no visible leaks could be detected.

A ‘Chilling’ Revelation

Thanks to the inherent high dynamic range of the Class C smart water meter installed at this location, WUS Experts were able to identify the source of water consumption: an industry grade ice machine. To determine that this was indeed the case, WUS Experts switched off the ice machine for one night:

With the right class of water meter accuracy, WUS Experts were able to identify that there was no leak by switching off the ice machine.