If you think about it, water births are done in what amounts to a warm bath. A warm bath in a normal tub can help your body recover. Swollen labia, haemorrhoids and episiotomy injuries can all be soothed by warm water. Tension and fatigue can be relieved too. Having a bath gives you some private time to yourself, and allows you to give control of your child to someone you trust, so that your mind can be free for a little while.
If you have had a c-section, it is better to wait for at least a week, so that your incision and stitches do not become infected during the healing period. Bathing with mineral salts has a slight disinfecting action, and it can help you relax.