I think the idea was that it is only effective for a short while. But yes, it does lessen the effect. Perhaps too much. I think the Rainmaker-spell should target the province of the casting mage only. Thematic reasons...
And warming the waters might not increase growth, as it is the cold water streams raising from the deeps at the shores of Peru and Norway that make the fish-population of those areas so rich. The spell itself seems quite right, though.
I don't like Steam. I could see it needing Air of Fire, but not Earth. Remember that Geysir, among others, is Water/Fire spell. Water/Earth would create mud, but that already is Earth-only spell. Maybe Water could, similarly, be the only path needed for the spells regarding Acids or maybe something else that could also need something else besides water. Acid might not be a good idea, though, as it would give Water
two different types of damaging spells, in the same path, one of which can not be resisted at all!
I like your 'flooding' spell, but the name does not suit it very well. I'd like to keep the Waterfall in the name, but can't come up with anything suitable...
A scrying spell or two seems appopriate for water. Astral should still have atleast one scrying, for Crystal Sphere if for nothing else, but it could have the risk of feebleminding the user.