water bath

from The Century Dictionary.

• noun A bath composed of water, in contradistinction to a vapor-bath.
• noun In chem., a vessel containing water which is heated to a certain temperature, over which chemical preparations or solutions are placed in suitable vessels to be digested, evaporated, or dried at the given temperature.
• noun Same as bain-marie.

from the GNU version of the Collaborative International Dictionary of English.

• A device for regulating the temperature of anything subjected to heat, by surrounding the vessel containing it with another vessel containing water which can be kept at a desired temperature; also, a vessel designed for this purpose.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A piece of laboratory equipment consisting of a heated vessel containing water, in which is suspended a flask etc that is to be subject to careful heating