For your cylinder you can either go Moist Water drop (very expensive), Moist Caliburn (not as expensive but still effective with crit), or stiff water drop (these are easily found in Shadow Cast City).
How is Moist Waterdrop more expensive than Moist Caliburn?
But yea, if Water Cannon is your main attack then you should really get Moist. I don't know about other servers, but in Ruairi they sell for under 100k so it's not too hard to get. If you can manage, go for Royal Alchemist since that adds very substantial boosts to alchemy.