Memory Dust

Memory Dust is a special magical powder of unknown origin that can erase the memory of magical or non-magical beings. It takes affect after the being goes to sleep and them awakens. It is first mentioned in the Season 2 episode P3 H2O when Patty Halliwell's Whitelighter Sam Wilder uses it to erase the memory of the Charmed Ones in order to protect them from an impending attack by the Water Demon that killed their mother at Camp Skylark. The victim's memory can simply be restored if a weak enough dosage is used - a weak dose was given to the sisters, ultimately allowing them to regain the memory of the Water Demon. Phoebe Halliwell then uses the dust on the kids at the Camp in order to keep them from entering the water, to protect them from the demon that killed their mother. She douses them with the dust and says "Land good, water bad".