Can I wire a water heater and tanning bed on the same 220V circuit?
The 2014 NEC is adopted in Ohio.

You need a dedicated circuit for these appliances:
Refrigerator, Freezer, Electric range, Microwave, Water heater, Washer, Dryer, Dishwasher/garbage disposal, Furnace, Heat pump, Air conditioner (central and window), Sump pump, Hot tub/Sauna/Jacuzzi 

A furnace requires a dedicated circuit.[422.12] 

Dwelling units require at least one receptacle outlet for the laundry area. [210-52(f)] Laundry receptacle outlets in dwelling units must be fed from a 20-ampere branch circuit. Receptacle outlets outside of the laundry area are not permitted on the laundry circuit. [210-11(c)(2)]

If an appliance is a chord and plug type and it exceeds 80% of the branch circuit rating then a dedicated outlet is required. If the appliance is fastened in place and is rated for more than 50% of the branch circuit then that circuit must be dedicated. [210-23(a)]

Here is a terrible reference, but:
http://electrical.about.com/od/appliances/qt/DedicatedCircuit.htm makes a good point, "A good rule of thumb is that if it has a motor, it needs its own circuit."