A bath actually uses much more water than a shower does.
If you fill the bathtub up fully with water then you use more water than it would take to take a 10 to 20 minute shower.
I tested this one time and plugged my bathtub drain while taking a shower and in a 10 minute shower the bathtub only had around 2 inches of water in the tub.
In a 20 minute shower the bathtub only had around 4 inches of water in the tub.
When I take baths I like to have the bathtub full of water so that I can soak in it.
I usually take showers to get clean but sometimes it's nice to just fill the bathtub up with warm water and then lay back and soak in a warm bath of water and bubble bath soap.
So taking a bath uses more water than taking a shower does.