How can I pass utility costs to the tenants?

[Steve Yoder]

In most of my buildings the tenants pay for their own utilities.  However, in one of my multifamily buildings (24 unit) I pay for both the water and heat (gas) which is costing over $55/month/unit.  It isn't cost effective to install individual water meters or individual gas meters.   What have you implemented to have the tenants share the responsibility for water and/or gas usage?  What has or hasn't worked for you?