Benjamin is a keen member of my Online Model Train Club and sent in this idea:

You might have seen those steel bands holding water tanks together. Well, you can add realism to your tanks by replicating those steel bands. The easy way is to get your hands on some copper-tone or black colored automotive pin stripe from an auto store. The good thing about pin stripes is they are perfectly straight which is near impossible to achieve with a paint brush and shaky hand. Also they come in a range of widths and colors. Although the tanks in the photo are not water tanks, you could use the same technique.