Giant Growth is best used during the declare blockers step when, after your opponent has declared who blocks this round and you receive priority again to play spells or abilities, yousqueezein the 3 damage to win the match with your Giant Growth.
Dry water resembles a very fine powder (like icing sugar or flour) that has a slightly more liquid-like appearance when it flows, and if yousqueeze some of it in your hand hard enough the powder combines to give you a few drops.