duplex with single water heater, shared water & gas

[Peter Perreault]

I'm looking at a duplex with a single water heater providing hot water to both units. They also share water and gas meters. Electricity is split. I'd like to understand the difficulty and cost of adding a 2nd water heater so that each unit has it's own and if possible splitting the gas. Short of getting a contractor involved, are there questions I can ask the owner or things to look for on the property that will help me to get a rough idea of what would be involved? Or is there a general rule of thumb for this?

thanks