He said the continuous flow on my meter was the drip zone on the maple and a subsurface line under the bluegrass, running all day and all night, and the spikes at two in the morning were the spray heads coming on. He said that the canister in the valve box was a fertilizer injector, which put liquid fertilizer into the irrigation water, and that there was no backflow preventer anywhere on the blue line, not in the trench, not in the box. He said that meant the irrigation system and my house's drinking water were directly connected, with nothing in between to keep what was in the irrigation system from going backward into my pipes. He said that the moment someone closed my curb stop and let the pressure in my service line drop, and then somebody in the house opened a faucet, that line could start pulling water backward out of the irrigation system, fertilizer and all, toward my kitchen.
"It's called back-siphonage," he said. "It's the whole reason the backflow rules exist. People have died from it. Not usually from lawn fertilizer. But people have died."
Then he looked at me.
"Mr. Osgood. Your house was built in 2014, wasn't it? Up against the open space?"
"Yes."
"Then you've got a residential fire sprinkler system. Town requires them in the wildland interface. It's fed off your domestic line. Red riser in the basement, by the water heater."
"Yes," I said. I thought of the gauge on the riser with its needle sitting on zero. "I saw it this morning. It's reading zero."