Hi English Daisy
The only way I know of to check on how many Thomas's may possibly have lived at Water Street in 1837 is to look at the 1841 census entries for Water Street. Fortunately I have access to this. The only other John Thomas I can find is aged 60, a Mason, living on his own. There is no record of the John Thomas, printer but as the first record I have for him is 1844 he may have moved into Water Street after 1841, in fact it looks like this John Thomas appears in the 1851 census at Water Street as a bookbinder as Head of the family (age 23) with sister Catherine Thomas (30) Dress Maker, sister Mary Thomas (possibly 30, possibly a Grocer, difficult to make out), sister Esther Thomas (age 29, Domestic Duties) and bother Henry (?) aged 17 (?), Printers Compositer, all have possible birth place of Llanwinio Carmarthenshire.
Where does your reference to John Thomas of Water Street come from?
My link in on my grandmother's side. John was a brother of William Thomas (father of both was Jonah). William Thomas and Margaret Williams produced a John Thomas! John Thomas married Sarah Edmund and produced Margaret Thomas. Margaret Thomas married Walter Rees who produced Sarah Elizabeth Rees my grandmother.
Roy