The shower only if it is a navy stlye shower where you turn the water off to put on soap and the on again to rinse.
honestly i tried this at home... measure a normal bath and mark the tub. Then next time you have a shower put the drain plug in shower as normal and see how much water you use. In our house we found we preferred showers as time saving but were suprised to find that they used the same or just a bit less water than baths do.
But just on the fun side of green, For a family of three or four, have each peson use the same bath water so everyone is good and clean just like the good old farm days, then using a 5 gallon pail, move the water from the bath to the washing machine add 1/2 cup of baking soda and a bit less detergent and wash a batch of clothes. and now you have really saved!
The average shower uses 7 gallons of water per minute. The average shower time being 7 minutes equals 49 gallons for one person.
The average size tub with hold 40 to 60 gallons when filled to the top but mostly we use 30 gallons. and maybe another 5 gallons to rinse off. so a total of 35 gallons.
Military soldiers are only allowed 3 minutes to take a shower for a total of 60 gallons of water per person. as their average shower usage is 15 to 20 gallons of water per minute.
For myself I do a 3 minute shower and find it is a great time where as my wife will be in there for 10 to 15 minutes. My 13 year old spends about 7 minutes and my 9 year old in and out under 2 minutes.
So in one night we are using 189 gallons of water to clean 4 people.
So depending on your shower times the bath could use more water then again it could use less. if you take a 2 minute shower you would use 14 gallons where a tub would be 30 gallons. If you take 5 minutes to shower you would be useing 35 gallons where the tub would be using 30 gallons. Some showers have a water saver built in to make them run on 2 gallons per minute and some shower could use up to 20 gallons per minute.
So I would say the tub would always use more water then a shower but it depend on your shower times.
a bath is not just a way of cleaning scum off one's body. (Indeed, some bath detractors would say it's a way of soaking in scum.) A bath is therapy, warmth, relaxation, a time to read, reflect, go back to the womb for a half hour or so.