Water Blades work good. Just make sure your paint is really clean when you use a Water Blade. You should wash it with a mitt or Sea Sponge. Water pressure alone won't get the paint clean enough to use a water blade. If there's any dirt on your paint, the water blade will drag it across your paint.
On plastic use 303 Aerospace protectant, to protect and restore, but it's not too greasy.
For bad water spots read this, from the Exterior Detailing sticky
Detailing your vehicle (Exterior)
On glass, you can also use Chrome polish to remove water spots. Search this forum I have posted info on it before.