33000gallon excess on water bill

On my most recent bill our water bill shot up to over 33000 gallons used. We live in a 4 bed/3 bath house in Florida. I’ve inspected all connections inside the house (toilets, faucets, showers, washer connection, etc) the only hint of a leak looks like some sort of relief valve next to the isolation valve outside as pictured. Could this be the cause and if so how do I fix it. New homeowner so I’m not quite sure what to do besides calling a plumber which is my next step.