Actually you can do a lot with water main, there are infinity combinations. If you consider water main as position 1 for example, excellent ninjas with such formations are:
Madara 5 kage, Sakura Summer, Kurenai, Sakura Cloak, Edo Itachi, Kisame, Minato Hokage, Gakido, Masked Man, Ningendo, Chiriku, Sai Suit, Sasuke Suit, etc. Basically ninjas that can buff your water, plus give you some safety just in case your opponent goes to strike her down. Water main is squishy in general, so you either need a ninja that removes all buffs with you or have ninjas that can fully buff and support her ( even if she's a supporter ninja in the formation).

Thank you!