When excessively worn, positive displacement meters tend to...

Positive displacement meters operate by physically displacing a certain volume of water, which is then counted to measure flow. When these meters become excessively worn, various components, such as gears or seals, may deteriorate or lose their efficiency. This wear can cause the measurement mechanism to not trap or register all the water flowing through the meter properly.

As a result, the meter might fail to account for the full volume of water that has passed through it. The gaps created by wear prevent a complete and accurate displacement of water, leading to the meter registering less water than has actually flowed through. This is particularly problematic as it results in under-reporting of water usage, which can have significant implications for billing and resource management.

In contrast, a meter that registers more than the actual volume or stops registering altogether would imply either over-activity or malfunction completely, which is not directly related to simply being excessively worn. Consequently, the choice indicating that worn positive displacement meters register less water than has actually passed accurately reflects the function and failure modes of these devices.