>Could I be being charged for the water heater?

Do you have a water heater in your unit? Then you're being charged for it. Unless this is a studio attached to a SFH and you're sharing a water heater (which seems unlikely since you mention "building management") you are absolutely paying for the water heater.

>I suspected that I may be being charged for the wrong meter, but I doubt it.

If you are living in a cold climate, that's unlikely because the usage would be quite low for someone living full time in their unit.