The Bath was added as part of The Bathroom Update (See also Toilet, Basin and Bin).
The Bath is a two block structure, like the bed.
It can be filled with 16 buckets of water, each bucket increases the level of the water in the Bath. To empty, just click with an empty bucket to take out a bucket of water.
The Bath has a similar functionality to the Basin.
The textures used are Quartz Blocks for the Bath, and Cyan Stained Clay for the handles and the faucet.
Five of any type of Quartz Block in a "U" shape at the bottom, and any type (not from other mods) Button in the top left corner (wood or stone), and you have a Bath!