you have to play tons of block to know it.
Mono-water simply isn't the best option, although you can play mono-water. It won't top an SJC, unless they run something nobody sees thats in water.
Mono water has no mid game like the good players said, hence the reprint of sea monster, even though i personally don't want a t0 ambush 5/0 sideways that can stall with another card of its own element to go into late game.
Water should be water/x, it has the best utility missions of the game right now. Show of power, arrogance, struggle, etc. All of these cards are relevant throughout the game state. All up to t6 with organization of peace, which is the most powerful utility card of water and card in block up to date.
Water isn't OP, the decks that utilizes water are op.