This modification will add a port on the side panel of your pack. It will also add a loop on the inside of the pack to hang a water bladder from. The port will allow a hydration tube to pass pass through to the outside of the pack. 
 
You will also have the option to add a mesh bladder sleeve on the inside of the pack for an additional $5. The mesh bladder sleeve will add about .5oz or so. 
 
This modification does not significantly effect the waterproofing of the pack. 
 
Adds about .1-.2oz to the overall weight.