Why is hydrosphere so good? - Heatshiver inquisitor

Character Level 94 Inquisitor Bandit: Alira Pantheon: The Brine King, Shakari
Pools 4,430 Life 1,970 Energy Shield 1,165 Mana
Defences 27,360 effective HP
Resistances 75% Fire 75% Cold 75% Lightning -17% Chaos
Weapon 1 The Annihilating Light Quarterstaff
Helmet Heatshiver Leather Hood
Body Armour Tabula Rasa Simple Robe
Gloves Onslaught Grip Stealth Gloves
Boots Ghoul Urge Sorcerer Boots
Amulet Entropy Pendant Jade Amulet
Ring 1 Mark of the Shaper Opal Ring
Ring 2 Death Gyre Two-Stone Ring
Belt Dusk Cord Leather Belt
Flask 1 Bottled Faith Sulphur Flask
Flask 2 Atziri's Promise Amethyst Flask
Flask 3 Taste of Hate Sapphire Flask
Flask 4 Medic's Granite Flask of the Skink
Flask 5 Quicksilver Flask of the Conger
Glorious Vanity Timeless Jewel
Watcher's Eye Prismatic Jewel
Armageddon Curio Viridian Jewel
Empyrean Blood Crimson Jewel
Body Armour Hydrosphere 21/20 Empower 4/8 Increased Critical Damage 20/20 Inspiration 20/20 Hypothermia 20/20 Increased Critical Strikes 20/20
Weapon 1 Frostblink 20 Bonechill 20 Arcane Surge 7 Inspiration 20/20 Ice Bite 20
Weapon 1 Assassin's Mark 20
Gloves Immortal Call 4 Cast when Damage Taken 3
Helmet Vortex 20 Increased Area of Effect 20/20 Ice Bite 20 Hypothermia 19
Boots Zealotry 20 Hatred 20 Discipline 21 Enlighten 3
Mark of the Shaper Summon Volatile Anomaly 20