In fact I have a vague recollection of our family depending on the copper for hot baths but much stronger memories of the copper being fired up to boil the bed linen in times prior to the exciting day our first washing machine arrived. Saturday night was our bath night too, and Bruce may well be right in surmising that was because of Sunday being church day. I seem to recall that Saturday was bath night for most people.
We had a neighbour in our small town who had the unenviable job of driving a horse-drawn open dray from door to door overnight on one night per week, to collect the nightsoil (a.k.a. poos and wees) from each household. His task was to remove the open can from the out-house of every household, tip the contents into the dray and return the can to be re-filled during the ensuing week. One assumes he didn't exactly smell of roses by the time he returned home at the end of his night's work. Anyway, it was well known that our neighbour didn't have electrically heated hot water and could only take a hot bath after boiling the "copper". Nightsoil collection was Wednesday night. Smoke emerged from our neighbour's washhouse only on Saturday nights.