I bought a new water heater(Bradford White) and installed it. When I went to throw away the box the water heater came in I saw a notice on the box that stated:
SCAQMD Rule 1121 Notice:This product is manufactured for sale subject to a product variance. It cannot be sold or installed within the SCAQMD after December 31,2007
You must be in California and that must be a gas heater.
SCAQMD stands for South Coast Air Quality Management District, and the water heater emissions must exceed air quality limits there.
It obviously is allowed to be installed under a variance until Dec. 31, so you should be O.K.