Chlorine breaks down organics (that's what we like about it) and in the process forms chlorophenols, which are carcinogens. The verbotten aspect of tap water in humidifiers doesn't, however, revolve around chlorine. It has to do with dissolved solids in the water. As the water in the humidification device evaporates, it leaves behind the solids, clogging the carrier media. Exactly the same process occurs in distillation: The water vapor is solids-free, the solids collect in the pot. Check your tea kettle, it probably has a white coating of solids inside.
For humidification/dehumidification of pipe tobacco, I use the Boveda packets. The humdity level is selectable, and they work both ways: If the tobacco is too wet, they absorb, too dry, they evaporate. Works for me.
For larger-scale humidification, like bringing whole leaf into case, I use a big mylar bag, 1/2 sheet baking trays and a cooling rack with wet sponges.
Baking tray on the bottom with wet sponges, cooling rack on top of that to provide space, another baking tray on top with the leaf. All stuffed into a mylar bag. Spong in with the leaf is there to keep an air space above the leaf and allow for air circulation. Set on top of a space heater on low. Takes a couple of days to bring crispy leaves up to nice pliability. And it smells soooooo good in there!