The source of the water coming into the Bath has never been properly established, and may have varied over time. [Strand Lane Bath, Statutory Planning File, London Metropolitan Archives, LMA/4441/01/0109.] In the mid-19th century it bubbled up through a hole in the floor, where patching to the brickwork can still be seen. In the early 1920s it entered at the north-east corner, but could also be seen seeping through the adjacent sides of the bath.
Since the mid-1920s it has entered via the settling tank at the east end. The supply has been interrupted several times in the twentieth century, for instance in the 1940s when the bath was derelict and blocked by rubbish, and again in the 1970s thanks to building work on Surrey Street.