The recipient of a water breathing spell is able to breathe under water freely for the duration of the spell--i.e., one hour for each experience level of the caster. The priest can divide the base duration between multiple characters. Thus, an 8th-level priest can confer this ability to two characters for four hours, four for two hours, eight for one hour, etc., to a minimum of one half-hour per character.
The reverse, air breathing, enables water-breathing creatures to survive comfortably in the atmosphere for an equal duration. Note that neither version prevents the recipient creature from breathing in its natural element.
