"Feel like a nice cool glass of ice water? Before you take a sip, you might want to take a quick tour of your home. How’s the fill valve in your toilet? Do you have a vacuum breaker on your outside spigots? What about your boiler?"
"Without the right plumbing bits and pieces in place, you could be at risk of drinking toilet water, sipping lawn fertilizers or slurping hazardous chemicals. If they aren’t protected, cross connections between the drinking water in your home and nonpotable water sources can mean that dirty water gets mixed with the clean. It might take as little as a change in water pressure.
And it’s not just in your home. Backflow can happen almost anywhere — from schools to restaurants to water treatment plants."