There is a long, thin, rubber-y line wrapped around/connected to the water line pictured below.
Other angle:
The piece in question is loosely hanging via a zip tie on my main water line about shoulder height and can be moved up/down easily.
It’s not the true actual usage. The water usage is recorded directly by the meter and should be accurate but sewage usage is not metered at all. They just assume that all the water you use will end up down the drain or down a toilet in your house so they bill you for the exact same volume of both sewage and water. This can get very far out of whack if you’re using a lot of water outdoors (filling up a swimming pool, watering your garden, washing your car, pressure washing for outdoor cleanup, etc).