Excerpted from Marketplace of the Marvelous: The Strange Origins of Modern Medicine by Erika Janik, out now from Beacon Press.

Today, when it seems that most Americans carry a water bottle to drink their eight daily glasses, the importance of water to health seems obvious. But for 19th-century hydropaths, water was more than just a sugar- and calorie-free drink: It was a social good able to cure nearly every disease as well as the social and cultural ills that threatened the health and stability of the nation.

Drinking was not the only way to enjoy water’s munificence, though; water was also to be experienced through elaborate rituals of bathing, showering, soaking, sweating, and wrapping. This diversity of baths, not to mention the idea of bathing itself, was highly unusual for most Americans. In 1835, a letter from a reader in the Boston Moral Reformer asked, “I have been in the habit during the past winter of taking a warm bath every three weeks. Is this too often to follow the year round?” Although it offered cures for disease, hydropathy functioned more as a water-based lifestyle plan with a vision of radically transforming the world through personal health achieved through nature’s purest substance.

Hydropathy grew out of the observations and experiments of Vincent Priessnitz. A peasant born in 1799 on a farm in Grafenberg in Silesian Austria, located in today’s Czech Republic, Priessnitz discovered water’s potential as a cure-all after an 1816 farm accident. One day while he was baling hay, a runaway horse and wagon trampled the teenaged Priessnitz, leaving him with several broken ribs and a bruised left arm. The doctor from a nearby town told him that the severity of his injuries made it unlikely he’d ever work again. Priessnitz, however, refused to accept this prognosis. He wrapped himself in wet cloths and ate very little while consuming large quantities of cold water. To reset his broken ribs, he pressed his abdomen against a chair and inhaled deeply, allowing the expansion of his chest to push his ribs back into place. Priessnitz eventually recovered from his injuries, and the success of his self-cure led him to broaden his investigation into the curing power of water.

Priessnitz sought not only to wash disease away but to deny it entry into the body through a healthy lifestyle of diet and exercise. Priessnitz argued that filth and a poor diet gave disease easy access into the body. In The Hydropathic Encyclopedia, American hydropath Dr. Russell Trall explained that disease was “produced by bad air, improper light, impure food and drink, excessive or defective alimentation, indolence or over-exertion, [or] unregulated passion.” For Trall, it all boiled down to “unphysiological voluntary habits.” In other words, sickness resulted from laziness, a lack of exercise, and junk food, the familiar chords of obesity debates to this day.

Perhaps hydropathy’s most visible legacy is in the popularly held belief in drinking eight glasses of water a day. This notion was appropriated and echoed with increasing fervor in the late 19th century by the temperance movement. By the 1910s and 1920s, American newspapers and magazines were filled with exhortations to consume eight glasses of water for health on a daily basis. Although scientists and doctors continue to disagree over how much water is enough, the idea of drinking fluids regularly for health remains undisputed.

Priessnitz’s water cure became renowned throughout the Western Hemisphere. Visitors marveled at Priessnitz’s ability to diagnose disease and devise a treatment plan simply by studying the quality and cast of a patient’s skin. He never checked the pulse, looked at the tongue, or asked patients about their complaints. By 1840, nearly 1,700 patients per year sought treatment at Grafenberg.

Priessnitz’s success spurred countless imitators and admirers. The first water cure in the United States opened its doors in 1843, followed by a second the next year. Both were in New York City and were operated by disillusioned regular doctors. But it was Mary Gove Nichols and her husband, Thomas, who made hydropathy famous. Born in Goffstown, N.H., in 1810, Mary Sargeant Neal was the precocious daughter of a freethinking father who encouraged her active and curious mind. As a teenager, she pored over the pages of the books her medical-student brother brought home, fascinated by the workings of the human body but perhaps also wondering why she could find so little information on the health of women like herself.

An unhappy marriage in 1831 to Hiram Gove, who disdained her reading and creative writing, helped turn Mary into a champion of women’s rights and a prominent health reformer. To ease her mental and physical suffering, Mary defied her husband and turned back to the medical books that had so enthralled her as a child. She discovered Sylvester Graham, an early advocate of dietary reform, vegetarianism, and hygienic reform and determined that women’s well-being and happiness depended on the freedom achieved through personal health. Excited by her newfound knowledge, Mary wanted to tell other women of the salvation that could be found in knowing about and taking charge of their own bodies.

In 1838, Mary made a name for herself lecturing (a scandal in and of itself for a woman) on the shocking topics of women’s health, anatomy, and physiology. Women’s health was a topic rarely, if ever, discussed at the time, much less in public. With no female regular doctors, many women ignored their own health problems and endured in silence to avoid being seen by male doctors, which social mores deemed improper. Hundreds packed lecture halls to see the thin, dark-haired woman with an open and intelligent face and exuberant brown eyes discuss the healthy female body.

In the summer of 1845, finally free of her husband, Mary traveled to Brattleboro, Vt., to investigate Priessnitz disciple Dr. Robert Wesselhoeft’s Hydropathic Institution—one of the most exclusive and expensive water cures in the United States. Impressed by what she saw, she began training as a water-cure physician, offering physiology lessons to patients in exchange for her education.

While Priessnitz’s original system called for water to be used both internally and externally, most American hydropaths believed that water worked best when applied gradually through the skin. The wet sheet became the standard method of application. First, the attendant would dip a sheet of cotton or linen in cold water and spread it on several thick wool blankets. The patient would then be wound up in the sheet and blankets by the attendant and secured with pins or tape. Once wrapped, patients would shiver and then lie sweating on feather beds for anywhere from 25 minutes to several hours depending on the seriousness of the illness. After they worked up a good sweat, the attendant unwrapped them and plunged them in a cold bath followed by a brisk drying. For severely debilitated patients, the wet-sheet treatment could be too much, so an alternative known as the wet dress was used instead. A loose-fitting nightgown-like garment, the wet dress allowed patients to dispense with the services of an attendant and to walk comfortably while also soaking up water. Most wet-dress patients also went to bed in the outfit, a damp and presumably clammy night of sleep.

Wesselhoeft taught his students, Mary among them, the art of individual prescription, adapting cures to each patient’s symptoms, stamina, and age. “The same treatment that would cure one might fail entirely with another,” she later noted.

After three months in Brattleboro, Mary moved to New York City in 1846 and began giving lectures and writing articles and books on health and hydropathy.

Though she’d never attended medical school, by the late 1840s, she led a doctor’s life and had earned a reputation as a trustworthy medical expert. Mary’s husband, Hiram Gove, finally consented to a divorce in 1847. That same year she met a young writer named Thomas Low Nichols, whose writing and progressive views on women she admired. The two married the following July. Inspired by his new wife’s work in hydropathy, Thomas enrolled in medical school to study “the very errors and absurdities” of regular medicine, graduating from New York University with his medical degree in 1850.

Most hydropaths believed that the only qualifications necessary to practice should be a personal commitment to the principles of hydropathy and a willingness and ability to practice them responsibly. Unlike regular medicine, hydropaths de-emphasized the authority of the physician in favor of creating independent patients able to diagnose and care for themselves. Patients thus had a substantial responsibility for their own outcomes. “If a patient thoroughly understands his or her disease, and has the requisite energy to accomplish a cure,” wrote Mary, “it may be done almost anywhere, and with very meager advantages.” She recounted stories of female patients who managed to heal themselves even while weak with disease through their own “indomitable energy.” Hydropaths believed that hygienic habits were best mastered through willpower and self-control, an ideology that mirrored wider societal beliefs about personal responsibility and social improvement.

In 1851, Mary and her new husband opened the nation’s first hydropathic medical school, the American Hydropathic Institute, in New York City. Concerned about the dangers of the misapplication of cold water, not to mention charlatans masquerading as hydropaths for profit, the Nicholses believed that the potency of water required expert guidance. More than teaching about water, though, Nichols wanted to provide a medical education for women to meet the national demand for female doctors.

With few exceptions, most of the nation’s medical schools refused to admit women. By and large, regular medicine tended to regard being female as a disease in and of itself. At the American Hydropathic Institute’s inaugural ceremonies, Mary delivered an address entitled “Woman the Physician” that argued for the importance of female doctors. Rather than reject cultural assumptions about women’s caring nature, she claimed women’s innate talents uniquely qualified them for the profession. The Nicholses’ progressive views of women aligned perfectly with hydropathy’s expansive understanding of women and women’s health. Hydropaths shared their era’s belief in women’s softer, more caring nature: They just did not see this as a justification for keeping women out of the medical profession.

Encouraging women to get involved in hydropathy contributed to the financial health of the nation’s water cures as well. To attract women and their money, hydropaths needed female attendants and practitioners to serve them. Women consistently outnumbered men in attendance at hydropathic institutes. It’s not hard to imagine why. For many women, visiting a water cure was the first, and perhaps only, time their needs were put above those of their husbands and children.

Hydropathy took the radical step of naturalizing women’s life stages. For hydropaths, puberty, menstruation, childbearing, and menopause were not dread diseases needing intervention but natural processes in a woman’s life. Women did not become weak and ill because of their sex but because of some outside cause, just like men. Hydropaths urged women to take an active role in their own health and to maximize their health and happiness through diet, exercise, and other hygienic practices, all of which dramatically expanded women’s power to determine and control their own lives. As a result, hydropathy provided a refuge for progressive women, and many of America’s first generation of female doctors came out of hydropathy.

Excerpted from Marketplace of the Marvelous: The Strange Origins of Modern Medicine by Erika Janik, out now from Beacon Press.