Stormy - Sorry this happened to you; it's bad enough when they are lost to predators...I feel your pain... One way to prevent this kind of accident from happening again would be to prop your waterer up on bricks. We have done this since we first brought chicks home last June, to help keep the water trough junk-free, and it works pretty well. As a bonus, there is always a firm surface to lay the water container on, and no digging underneath.
Just a thought - your chick may have dug under the waterer after you placed it back in the coop because it was cool in the pine shavings there, and was unable to get back out.
Hope this helps!