Yep, been there, done that, have the scars to prove it. Long, sad story--basically I screwed up.
Bout the only way to deal with anything wet is put it in a COLD pot. Then as the lead comes up to temp the liquid (water, antifreeze, oil, whatever) will vaporize before you get to the temp needed for the lead to melt.
NEVER, NEVER, NEVER add the wet, damp lead into the hot pot! Clean the melted lead, cast, then let it cool completely down (next day) and you can again deal with wet lead.
This is why I don't wash mine--too likely to get some liquid hidden in some small nook or cranny--only takes a drop and then it's like holding on to a gernade when it blows.
ÇR