Communal electric use, but only having 2 meters on duplex.

[Nicholas Ostrem]

Hello,

I have just purchased my first duplex and been going through the place and noticed that the lower unit is paying for communal electricity (Washer/Dryer, outside lights and anything plugged in the basement). 

My question(s) is, what is seen as the best way to separate the usage? Do you spend the money on a house meter, get a sub meter installed? What have other people done?

Thanks for the help!