Increases the effectiveness of your healing spells by 25%, the healing done by your Water Totems by an additional 50%, and the healing done by your Healing Rain by an additional 100%.
In addition, heals you cast increase allies' maximum health by 10% of the amount healed, up to a maximum of 10% of their health.
Purification is a passive shaman ability learned at level 10 for those with the restoration specialization. It increases the healing done by all healing spells by 25%, and increases healing done by water totems by 50%. In addition, heals also increase their target's health by 10% of the amount healed, up to a maximum of 10% of the target's health.
The 'effectiveness' part in the tooltip can be somewhat misleading, as it refers to healing done only. It has no effect on the mana cost of any spells, though a 25% increase to healing done is technically also a 25% increase to healing-per-mana.
Purification is applied after spell power, meaning that it effectively improves the scaling of all healing spells. Overall it is a significant boost to healing.
While it is not a shaman spell, Lifeblood still benefits from Purification.