Yes, for the water part of the vault, I think we should analyze which cards are the most usefull.
That gives 24 of: squids, toads, dragons, crawlers, chrysoara.
18 of: Mind Flayer, Freeze, Ice bolt
15 of: Ice shield, Steam machine
12 of: Trident, Nymph tears, Purify
6 of: Flooding
0 of Nymph Queen (unless someone actually has one)
The rest of the 50% water cards (and maybe more) can be filled with penduli, and some pillars. (Penduli are most usefull, because they can always be used with a watermark if needed).
Also, penduli can help to get a 50% water deck, for example in the following deck are more active fire cards then water cards, but because of the water penduli, there is still 50% water:
2 Rain of Fire
2 Deflag
6 Rage potion
6 Steam machine
2 Ice shield
12 water penduli
Mark of Fire