For water main, it's so hard to build team, coz if face fire main, water main is in disadvantage.
currently I use water main too by build up formation:
Tenten GNW Water Main X
X X X
X Tobi Iruka

the main dmg is 10 combo chase.
Tobi can do his mystery in 1 round by 10 hit, 10 combo chase can active.
I hope this formation can help u.