Abstract
Intermittent supply is common worldwide. It triggers households with piped connection to adjust the supply scheme by the use of a water tank with a float valve (FV) at the entrance, which has a major influence on the water meter accuracy. This study investigated the impact of the water tank with a FV on the performance of water meters under intermittent and continuous supply conditions, using laboratory experiments, field measurements, and hydraulic modeling. Results revealed that the inflow rates into the water tank are consistently lower than the outflow rates of the tank. This will always be the case owing to the balancing mechanism of the tank. The flows that pass through the water meter represent the inflows into the tank. Therefore, higher metering errors and more apparent losses are expected for a combination of a water tank, FV, and continuous supply. Besides, different FV types have different hydraulic characteristics. Larger FVs with higher discharge rates tend to maintain the water level close to the full level in the tank and conferred longer periods of low flows, worse meter performance, and more apparent losses. For intermittent supply, results confirmed that higher intermittency levels lead to improved performance of water meters and reduce the apparent losses. This points to the complication in transformation from intermittent to continuous supply worldwide. In this case, water utilities should expect higher meter errors and more revenue losses unless the meter replacement policy recognises lower flows passing through the meter.
Highlights
The water meter is a cash register, a system management tool, and a conservation instrument
This study investigated the impact of the water tank with a float valve (FV) on the performance of water meters under intermittent and continuous supply conditions, using laboratory experiments, field measurements, and hydraulic modeling
Higher metering errors and more apparent losses are expected for a combination of a water tank, FV, and continuous supply
Summary
The water meter is a cash register, a system management tool, and a conservation instrument. Water meters are not absolutely accurate measuring instruments. All water meters, including new ones, have drawbacks. Mechanical meters are commonly used to measure the water consumption for customers of water utilities. They are either volumetric meters that measure pockets of water directly such as rotating piston meters, or inferential (or velocity) meters that infer the volumetric flow rate from the velocity of the water, such as Woltmann, Single, and Multi-Jet meters. Electromagnetic and ultrasonic meters are marginal technologies that are used in limited, specific cases because of their high cost and power requirements. They detect water velocity using electromagnetic principles and ultrasound waves. Recommendations on the selection of the appropriate meter type are proposed based on the consumption data (Johnson 2001) and criteria that include low flow accuracy, ability to pass particulates, and accuracy degradation rate (Mutikanga 2014)
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