This is a billboard put up by Denver Water tell the public that they shouldn’t waste anything, and use only what you need because everything is valuable. Placed as a billboard along a road next to a express way to maximize exposure, and with the use of negative space works.

I believe this ad works because it’s almost completely visual and the impact it makes is great because most billboard ads take up the entire billboard where as this “use only what you need” bit with a space only large enough for the text only but leaving the rest of the the billboard bare.