Splitting Utilities Amongst Tenants

[Catie Fihn]

Hi!  Newbie landlord in Wisconsin here.  My husband and I are currently getting tenants in for our first duplex.  The duplex currently only has 1 meter for utilities.  

How do I go about charging the tenants for their electricity and gas?  We pretty much have our tenants in place.  The upper unit will be occupied by 3 young adults, and the lower unit will be occupied by 1 adult and her 4 children.  Of note, I believe the lower unit will mostly be 1 adult and 2 of her children, and the other 2 children will only be there part-time.

Do I just keep the electricity/gas in our name and have the tenants reimburse us each month?  If so, do I just email a copy of the utilities to all tenants each month and have them split the bill 50/50 (upper tenants pay 50% of the bill and lower tenants pay 50% of the bill)?

We will likely have an additional meter installed at the property in the near future so that each unit will have its own meter, but until then, I need something concrete in their leases to identify how the utilities will be paid.  And once we have the additional meter installed, I assume I would need to send an addendum to each tenant to sign, indicating the change in utility billing?