Andrea
There is no lead in a cast iron tub. Even if some could get into the molten iron, the temperature would destroy it immediately. Besides, unless the water were standing in the tub for an extremely long time, any impurities would not leach out, and additionally, you do not normally drink the water in the bathtub.: Is it true that old claw foot baths become porous once the enamal/porcelain has worn and leach lead into the bath water? If so, would some baths be likely to do this and not others dependent on manufacture date?
