Kneipp was a Bavarian priest and not a physician. He learned about hydrotherapy and other methods of treatment later called naturopathic during the time he suffered from tuberculosis. 

Digital facsimile of the 1889 10th edition from the Internet Archive at this link. Translated into Englishfrom the 36th German edition as My water-cure, as tested through more than thirty years and described for the healing of diseases and the preservation of health. Edinburgh: William Blackwood and Sons, 1891. Digital facsimile of the 6th edition of the translation from the Internet Archive at this link.