The following was reported in
The Birth Book by Dr. Sears

One study showed that women who were in the water for 30 minutes to 2 hours of labor dilated twice as fast (2-1/2 cm per hour vs 1-1/4 cm per hour), the babies descended twice as fast, and the moms experienced less pain.

The c-section rate was reduced by 2/3 in waterbirth moms. And water is especially beneficial for VBAC moms. An informal study of records from the past five years have found that use of medication (epidural or narcotic) with waterbirth mothers was cut almost in half.