@NeverDie Most all normal water meters use magnetic drives to isolate the register from the main flow (even the wet registers).
Common water meters are single or multi-jet Class A or B to actuate the magnetic disc but meter orientation alters accuracy. The positive displacement/piston variety simply rotates volumetrically so orientation does not matter. There are also ultrasonic types so again no contact, very accurate but crazy expensive.
The critical point is the K factor of the factory built meter, K=1 means 1 litre output. This is not something you can alter, eg My outdoors Zenith is a multijet with K=500, the sensor is about 50 euro, but a 5c reed fits just fine. Useless at 500 litre/pulse but it illustrates the point it's how the meter is built.
@OliverDog the V200 I have has a mosfet type sensor (triggered by an inductor?) rather than a reed, normally very expensive, but I got lucky with one supplier, from memory the meter and sensor were less than 100 quid, the battery for the sensor lasts maybe 10 years. If it dies I'll install a V100.
Modern versions such as the V200H are usually RF or cable to a specialist receiver but it starts getting complicated with proprietary protocols as they're really designed for the water service industry, although some wizzes have hacked various models. May be worth a google as I'm out of touch these days..
It may be an old Class D design, but the V100 I nearly bought instead has a plugged socket in which the reed is inserted into the meter body. The Elster official reed is expensive but you can slip a normal reed in with a bit of preparation, it works fine as did one for a friend. Pretty sure the V100 is now made in Malaysia by the ex-director or similar of Elster, demand in Europe etc for the drive-by reading capability and Class D has tilted the market. No idea whether the Chinese market has clones or they're made properly.
@NeverDie "A patent pending Flume sensor"... Flumes are restrictors for open channel flow measurement been around for over a century or more, a pipe version is called a Dall Tube, see Bernoulli's equation.
Sounds like marketing hype, but it's just mag measurement sent to an app.
A lot of folks have tried sensing magnetic fields or reading part of the register, think some on here had some success with photo sensors, so plenty of options...
