The Glorious Pool by Thorne Smith

Sixty year old Rex Pebble inadvertently discovers that the fountain of youth happens to be in his back yard swimming pool. A magical statue of a nymph by the name of Baggage, an ornamental pool decoration, has playfully endowed the Pebble swimming pool with the power to reverse the aging process. Typical Thorne Smith fun ensues when Pebble, his wife, and his mistress take a dip and take twenty years off their lives.