My dog does the same thing don't worry about it, I think its some kind of separation anxiety dogs have when their owners leave. Its not a big deal my dog has done it for years, he wont starve himself or anything. Hell eat eventually.
There are two reason, number one......your dog knows your not home, and also knows they can not get outside to go to the bathroom, eating or drinking will cause them to have to go to the bathroom. So they just wait. They are smarter then they seem. Number two.....Dogs thrive on attention when you get home and sit down to watch your movie and hear crunch crunch over in the corner, your dog is saying hellooooooo check me out.
Maybe it makes him comfortable when you're home. Because you are his friend it makes not fell alone. Maybe he's nervous when you leave him alone.