if u want to build up a great waterteam i can tell u some tricks. what u rly need is a ton of sealscrolls for kage tressure (lvl70)and every event that can give u tenten gnw. if ur lucky ull get chojuro or even mei. good chances that that u will drop ao in those 60 pulls for the rar. those ninjas will make water rly strong.
im not the biggest fan of neurotoxin for pvp unless u have godlike refine and chaos the whole team. u give up 40% dmg for that and often it gets cleansed right away. a weaker interupt from another ninja is good enough. i also use haku a lot. u can rly feel that 80% dmg buff.