You have to slowly learn a dog to be alone. That's something that isn't natural for them. They are pack-animals. Their survival and succes depends on the pack. Not in order anymore in this context, but they still have that pack-instinct. So you really have to teach them that beeing alone isn't going to hurt them.
How long it takes is different for each dog. Best to start with just seconds, then a minute, few minutes… and so on and on. But make sure you allways return before they start panicking. Giving him something to do will help. Having a constant pattern for leaving the house also helps. Saying the same words every time when you pick up your keys and put him in his bench. He then will know you are leaving and will learn that it's nothing to be upset about. But he doesn't know that now. So if you leave and he is sleeping, when he wakes up, he doesn't know what's going on and will panick.
If it is possible, you can maybe let him stay with your neighbours when you are at work the next few weeks, while you are learning him to be alone.
If he is panicking now, and you continue that way, chances are it's going to be very hard in the future to change that.
Quite frankly, I do NOT put water in a crate when I go to work [for the puppies]. What goes IN, must come OUT!
I would never put a puppy 8 hours in a bench without water!! If they are thirsty, he should be able to drink!