What does running water do to thaumathurgy? For example, the wardens sometimes throw big veils over buildings (using thaumathurgy). What would happen if it was a very rainy day? Does running water effect thaumathurgy at all, or is it just evocation?

I ran my first Dresden Files RPG last week and I have a couple of questions I'm struggling with, I am in need of advice.

First of all, my players love intra conflicts, so right of the bat they initiated social conflict with each other, both mainly using intimidation (the only social skill they have). But does this require Social Conflict, or would a simple Contest or Challenge suffice? They want to be a threat towards each other so I don't want it to just appear as roleplaying "fluff". I want it to have consequences and a real life feel to it. How is this best handled?

Secondly, they have used social conflict on a police officer to get them tear gas and pretty much rob the whole inventory blind for their conflict. She (police officer) conceded due to peer pressure to get only the tear gas and thus risking her career for them. That's where the session ended, but I'm positive they will ask her to help in the fight. And story wise, the police officer would want to do that and it would make sense. But how do you handle an npc in battle? Is she an aspect on the scene they can tag, does she actually fight like the other PC's do?
What if a whole police force surrounds the buildings to help fight the bad guys, how do I deal with it.

Also, like said above, they will acquire tear gas. How is this best resolved. As an environmental gas that attacks anyone in the zone, as a block from attacking or moving, or as a manoeuvre. Or as something else I've missed.

Last of all, I have the feeling my players go a little overboard with intimidating every person around them, does anyone have ideas how to encourage talking and normal interaction besides intimidating?

Thank you!