This one is about worm farms. Sorry , I myself know nothing about raised beds! Good luck

Describe the bed more. Is it in the ground, too? I mean, partially buried like commercial pits? Does it have a bottom or is it open to the ground? What are your goals with these worms? Compost, bait, cocoon production? What are you using for bedding? How many worms do you have? What do you cover the bed with?

I would add bedding at this point. Especially if you are using finished compost or aged manure.

You don't want to over water a bed. It leaches the vitamins and minerals you want. Top water. Some claim city water can be bad for worms. You used to be able to let water sit and the chlorine would gas off. Now many municipalities use chloramines, which don't gas off so readily. Supposedly these can hurt or irritate the worms. I have no idea if that is true, but I use rain water anyway. If you are using the bed for composting scraps and it isn't a big bed, the vege scraps may contain enough moisture to add most of your water. That also depends on the type of covering you use. The type of worm you use also determines moisture needs. Most worm farms water outdoor beds daily. Of course, they also use grains for feed at times, which dehydrate the soil (which makes corn gluten meal a good pre-emergent herbicide as it dehydrates seeds). Just don't flood it.

Essentially, you haven't provided enough info on your system to validate any advice anyone can give you. Could you provide us more details?