Waterbender prison

Hama's Prison, located on a remote island in the Fire Nation, is a maximum-security facility that was constructed specifically for detaining waterbenders. To ensure that none of the prisoners had access to water to bend, they were suspended in cages and dry air was pumped into their cells. Hama mentioned that before they received any water for drinking, the waterbenders were restrained at their arms and feet, and that any resistance or attempted uprising during this stage was met with severe consequences.

Trivia

 * It is here that Hama first discovers Bloodbending, developing and mastering the ability by practicing on rats. She escapes many years later by Bloodbending a guard to unlock her cell.
 * From Hama's flashback, it is generally assumed that her fellow Southern Water Tribe Waterbenders were held here as well.
 * From the scene right before the fight with Katara, Hama, in her anger, stated that only she made it out of the prison, and that all her fellow peers failed to do so (implying that they died), then said about the Fire Nation civilians: "They deserve the same fate!"