This is actually one of the large reasons that taking a bath (defined as submerging the body) was not common until the late 19th century with running water, and heated water, being more accessible. Prior to this most people washed on a regular basis out of a basin of water, not unlike we think of sponge baths today. To fill an entire tub would require a great deal of water carried in by pitcher or basin and the same way removed, not to mention heating all of it. Not very practical. Alternatives such as public baths were fashionable during certain time periods, those relying on springs for water source.