I am not sure what the rest of the state of Illinois did. What I know is, when I have gone on inspections, it is a state law to get the annual inspection of any back flow preventer. Off the top of my head, the only reason that a home would have a BFP is a sprinkler system (for fires) or an irrigation system ( for watering your lawn) there is so few of these in the village on residential properties .... I believe that it's like anything else, the water company is getting the information out that they asked the homeowners " do you have one or not? " and if you do, "has it had its annual inspection?" no one is coming into anyone's house.... I would think this isn't the first survey letter sent out, but I can ask.