The area around the trunk is designed to channel water away that runs down your back window and when you open the trunk. Whenever I wash my car, after blowing off excess water, I start a wipe down with microfiber towels by opening the trunk, letting water run down the channel on both sides, then I wipe down starting from the upper part of the trunk lid, all the way around to the area between the tail lights.
Hood area also has water channels, mostly the cowl area behind the weather stripping. What is very effective in the engine bay is Windex, the non-ammonia kind, which will get most water spots and any oily residue that's on exposed parts. Stubborn water spots usually can be removed with detailling spray, the same stuff you use on the finish. If you have a really stubborn stain on a metal part, or on any polished, satin or billit finish, there are polishes available that will take care of this in a snap. Lowes or Home Depot have stainless steel polish, and Meguirs (sp) has a metal polish. Both work great.
Watch out for dried coolant. It leaves a bright white spot or spots wherever it touches, some very tiny.