This is known as bikeshedding. Something like turning off water is something anybody (also the campaign agency) can comprehend. Turning off water safes water,

This is known as bikeshedding. Something like turning off water is something anybody (also the campaign agency) can comprehend. Turning off water safes water, easy. Now think about trying to reduce exhaust pollution, you can't see it, people don't know how much pollution is generated by a car, and most importantly: there is no easy solution to reduce it. Yes, you can ask people to leave their car at home and commute to work by bike, but that does not work for everybody and reduces comfort for most people. The campaign agency could have done an awareness for exhaust pollution, but that would have been much harder to do, and probably they won't make much friends while doing so. Where as something easy as a water saving campaign will give that loads of goodwill.