The relationship between orthodox (mainstream) medicine and heterodox (fringe) medicine during the nineteenth century continues to puzzle historians of medicine. Though many have qualified the sharp antagonism between the two as a (biased) historical construct, it remains difficult to lay bare the common problems that structured mainstream and fringe. In this contribution on the reception of hydrotherapy in the Belgian fin de siècle, I attempt to rethink the oppositional character of nineteenth-century fringe medicine at an empirical level. In many ways, I argue, Belgian hydropaths were prototypical proponents of medical heterodoxy, as they defended neohumoralist medical conceptions and shared an integrated Catholic "cosmology." Their moderate critique of bacteriological science, however, also echoed the unease felt by many established physicians. In their pretheoretical beliefs about the healer's intuition, they voiced traditional conceptions that stemmed not from the fringe but from everyday bedside medicine. The popularity of hydrotherapy, I argue, reflected one of many attempts to save a common "cultural doxy" shared by established physicians and heterodox healers alike, in the wake of bacteriology's analysis and standardization.