Sorcerers with the Elemental Bloodline have the ability to change damage type on spells that do energy damage to their bloodline type because of this:
Bloodline Arcana: Whenever you cast a spell that deals energy damage, you can change the type of damage to match the type of your bloodline. This also changes the spell's type to match the type of your bloodline.
In the glossary, "energy damage" is defined as being [acid], [cold], [fire], [electricity], or [sonic]. That means that the Bloodline Arcana would not allow one to cast Magic Missile which has the [force] damage type as a fire damage spell.
Snowball has the energy damage type of [cold, water].
Can said sorcerer cast a Snowball that does [fire, water] damage?
Best Answer
Yes, as that's what the rule says you can do. If you are having trouble visualizing it, "steam" might help.
You can freely have e.g. flaming and frost enchantments on the same sword - there's no "they cancel each other out" rules anywhere. If you allow it, you figure out how to justify/skin it, but combinations of "opposed" energies are completely rules-legit.
Note also that you're slightly confusing classically opposed elements like fire/water and earth/air with the D&D energies - acid, cold, fire, etc. Fire is both an element and an energy type, while water is only a descriptor and cold is a damage type and a descriptor. Water is in the spell descriptors but not the damage type; it's a spell with fire and water descriptors but a damage type of fire.