It’s important that the bedding/castings be moist but not soggy.  Worms breathe through their skin, and to do this it must be moist.  You want to keep the bin about as wet as a wrung out sponge.  Here’s an easy way to test your bin’s moisture level.  Take a handful of bedding/castings & squeeze.  If no water drips, it’s too dry.  If water runs out in a steady stream, it’s too wet.  And if water drips out in drops, it’s just right.

I keep a 5-gallon bucket of water for watering, next to the bin.  It’s convenient and chlorine dissipates from standing water.  Chlorine’s job is to kill microbes;  the composter’s job is to cultivate them.   The EPA’s website, however, says that chloramines, which some water companies use instead of chlorine, “does not rapidly dissipate on standing”.*

Any liquid that’s been in the fridge too long, other than citrus or salty, can be poured over the bin, adding nutrients.  I tend to err on the side of under-watering.  An overly soggy bin will not allow air to circulate, which is necessary for the worms and the aerobic bacteria.

*If anybody knows how long a 5-gallon bucket of water must stand before chloramine fully dissipates, please reply.