Increases the duration of your Summon Water Elemental spell by X sec and your Frostbolt spell has a Y% chance to grant the Replenishment effect to up to 10 party or raid members mana regeneration equal to 1% of their maximum mana per 5 sec for 15 sec. This effect cannot occur more often than once every 6 sec.
Increases the duration of your Summon Water Elemental spell by X sec and your Frostbolt spell has a Y% chance to grant the Replenishment effect to up to 10 party or raid members mana regeneration equal to 1% of their maximum mana per 5 sec for 15 sec. This effect cannot occur more often than once every 6 sec.
Enduring Winter (formerly Improved Water Elemental) is a talent in the Frost tree, you will need to spend 44 points in Frost to max it.
Patch 3.1.0 (2009-04-14): Renamed Enduring Winter. Instead of the Water Elemental increasing mana regeneration for the Mage's party, casting Frostbolt now has a 33/66/100% chance to provide the Replenishment buff to up to 10 people in the Mage’s party or raid.
Edit
Patch 3.1.0 (2009-04-14): Renamed Enduring Winter. Instead of the Water Elemental increasing mana regeneration for the Mage's party, casting Frostbolt now has a 33/66/100% chance to provide the Replenishment buff to up to 10 people in the Mage’s party or raid. 
