Healing magic is Water elemental magic and is mentioned by Zander in chapter 3.
Healing through Water magic is the 'Tamra' use of the element. Tamra is magic that isn't dangerous and doesn't hurt anyone. It is mentioned that Zander's teacher uses Water magic as Thallan (or the more dangerous form of magic), which has the capability to hurt people.
It is hinted that Zander himself knows Healing magic, for he healed Aida in chapter 2, but has since refused because she is 'impossible'.
Rin herself says in the library that Achemists are usually better healers than mages.