If you have a scout you should never have to cast rain while in combat. Rain doesn't put you in combat either, and with the huge radius you don't need to be in line of sight to drop it on a group of enemies before initiating.
Rain doesn't have an unlimited duration. Thus, you will end up casting it in combat, even if you scout ahead every single time. This is especially true if you cast multiple spells as a result of scouting (for example, Rain + summon); you'll have to pick one for the shorter duration.
I guess it's not crazy to get Rain on both casters. There are situations where as soon as the rain stops, you want it back up immediately. However, that isn't an argument for having two characters heavily invested in Hydro, it's an argument for one of them having 1-2 points in it.
This is actually really important. RAIN STACKS WITH ITSELF.
You can cast rain again on the same spot, and it will widen the puddle on the ground. I am not talking about the stat benefits stacking with itself, but creating a larger and larger elemental effect. Even if you cast Rain on the exact same spot, it will keep getting wider and wider.
I have filled entire screens before with electrocuted rain. Right now I am running two characters who have Rain at 1 Cooldown. You can never have enough rain. Just remember that electrocuting the water reduces the amount of rain, so you need to generate more rain than you are destroying. It's not a bad idea to give EVERY character Hydro 1, just for Rain and maybe Water of Life. Rain is just that good.
