Tech for one water meter on Duplex options?

[Brad Gilboe]

I have a duplex with a single water meter.  I remember an ad for a digital tech product that would track the water on individual lines to be able to accurately bill back to tenants.  Does anyone know what im referring to?

If not, how do you typically handle diff levels of usage of water for two units?  I have an upstairs unit with 2 adults and a child, and a lower unit with one adult.  Any help on best practices for structuring this is appreciated.  Thanks in advance.