The Water of Life was a poisonous blue liquid used by the Bene Gesserit to turn their Sisters into Reverend Mothers. To the untrained in prana/bindu body control, the substance was lethal; even the smallest amount will kill someone in incredible agony.
The Water of Life originated on the planet Dune. It began its life as the bile of a young sandworm, and, if it did not kill the Bene Gesserit or Sayyadina who ingested it, was converted into an awareness spectrum narcotic that was used in spice orgies.
The untreated liquid was retrieved from the sandworm as it was drowned in water. The liquid exhalation only emerged right before the creature's moment of death. The typical reason for performing such an act was for the purposes of elevation of a Bene Gesserit Sister to Reverend Mother status.
In Fremen culture the event took on a more urgent tone: it normally occurred when a Sayyadina was dying and a replacement was required to receive her genetic memory before her demise. Typically a woman would be chosen from within the tribe for this task.
In the Bene Gesserit tradition, the bile was fed to a Sister after she had received many years of training in prana/bindu body control. This was because it was only the Bene Gesserit abilities of altering metabolism and slowing heart rates that could possibly neutralise the lethality of the chemical. The Sister regresses into a coma-like trance, and converts the toxic elements on a molecular level. If the Sister failed to metabolise the chemical, the poisonous bile would kill her. Were the Sister successful, however, the process would amplify her awareness to the point where it would unlock her genetic memory, and along with it many secrets of the Sisterhood.
Upon completion, the converted sandworm bile was regurgitated by new Reverend Mother or collected from perspiration on her skin. The chemical collected then officially declared the Water of Life. In Fremen culture it was then consumed by members of the sietch. The narcotic qualities resulted in the sietch members partaking in a spice orgy.
The Kwisatz Haderach
Since its inception, the taking of the Water of Life could only be conducted by women appropriately trained in prana/bindu. Any man who had tried died. Bene Gesserit plans had it that the culmination of their breeding program would result in a male Bene Gesserit who could successfully convert the Water of Life. This man would be the Kwisatz Haderach. In 10193 AG, Paul Atreides was the first male to succeed in converting the Water of Life, in a process that kindled new and immense powers in the young Atreides Duke. Before, and even after this attempt, many men had attempted the process and died. Paul had consumed only one drop of the bile, and it had put him into such a deep coma that he was believed dead. After three weeks, however, he emerged, having successfully converted the bile into the Water of Life. Along with it came many powerful abilities, such as perfect prescience. Paul informed Chani and his mother that not only could he see the past and future, but also the present, into the space above Arrakis, where the Emperor's invading fleet was orbiting the planet.