Soon after it gained independence, modern India outlawed discrimination against so-called "untouchables," the lowest of social classifications outlined in Hindu scripture.
In reality, hundreds of millions of Indians continue to be ostracized and mistreated because of their connection to that class.
Night soil scavengers
By day, millions of Hindu faithful have come to bathe in Ganga water over the centuries, but this plunge in the water has a special significance for one group of women.
Their journey starts in New Delhi, at the headquarters of the Sulabh International Social Service Organization.
This is a refuge for women who were born on the wrong side of Hinduism's ancient caste system of social classifications. For thousands of years, they and their "untouchable" ancestors have had no other life option, but the lowest of the low-caste professions - night soil scavenging. A polite euphemism for the manual removal of human excrement from primitive dry toilets.
Usha Chamour says she was seven when she started following her mother around so she could watch her clean night soil and learn how to do it herself. Her mother carried the waste on her head, and she says she would eventually have to do the same thing herself. She says her hands were too small at the time for the usual cleaning brush, so she had her mother make her a miniature one.
Nightsoil scavenging is slowly becoming obsolete in some areas, thanks to a sanitation revolution launched by Bindeshwar Pathak. He developed, an eco-friendly, underground toilet system which he calls Sulabh, meaning "simple." It converts waste into dry fertilizer and biofuels inexpensively and with no daily maintenance.
"We took him to hospital, and the boy died. There, I took a vow to fulfill the dreams of Mahatma Gandhi," he says.
Pathak now offers these women an escape from untouchability, and their first experience of a classroom.
"My name is Dolly Parwana. I live in Tonk, Rajasthan. I joined Sulabh in 2008," a new student tells her classmates. "I love reading in English. I read every day English paper. And-- that's it."
A Sulabh English teacher says her students are in love with learning.
"These children, they are coming from the area where they have zero education. They are very smart, very intelligent. Age is no bar," she explains. "I meet ladies who are almost sixties, 67, and they come very sweetly and they say, 'I don't know how to write my name-- can you please teach them?' The shine which comes into their eyes that they have learned how to write their name-- it really gives me encouragement to learn from them."
Pathak, Sulabh's founder, hopes all of India will learn something from these women about redemption from the past. He takes them on high-profile, made-for-media excursions around India and the world.
On this latest trip, they pray at holy Hindu shrines. They receive songs of blessing as they sit side by side for a meal with members of Hinduism's highest class, the Brahmins.
"More than 200-million people or 300-million people, they are not allowed to have food with others, even today," he explains. "If you go to the village, they cannot have common dining."
Sulabh is slowly changing Hindu attitudes, as some of the conditions that fostered untouchability are replaced by better hygiene and sanitation. But volunteers say plenty of work lies ahead, because attitudes 5,000-years old are not easy to wash away.