Note that this compartment is not totally sealed off from the photo compartment below. The base flap is zippered along three sides and has gaps at the turning corners when closed.

To store a water bottle here, take an extra precautionary measure like putting it in a Zip-Loc bag or an air-tight container first.

This unique design also allows the 3n1-20 to be converted to a long lens case. After some rearrangement of the dividers in the photo compartment, a dSLR attached with a bigger tele-lens can be accessed via the top compartment with its base flap raised.