What kind of dye did you use? Were customers not concerned about dye in the water? Is it easier to see the dye at night? (your lucky you have no ice!)
We use a method we call valve "squeeling" go to the suspect area and close the valve that shuts it off. Wait about 30 minutes. If the line leaks the water will empty from the line. When you open the valve you should hear the water rushing back to fill it...we have a natural occuring chlorine and the chemical packets will give a positive result so for us it's unreliable
With "squeeling" I guess you would have to shut off all the connections (houses, farms) to the main line before you begin? We have some farms that are taking water at all times of day (filling reservoirs in the middle of the night).
Put it in a new valve midway between your existing isolation valves to isolate leak, or if you have a correlate, use a vac truck to suck down to your pipe for a contact point with less distance then your isolation valves, when u fill the hole back in use a 2 nick plastic pipe on top of the pipe so that in the future u can make contact without having to use a vac truck again if you need to leave it below grade then cover the pipe with a tin can do u can locate again later with metal detector
So it turns out after looking all winter on and off for our water break, someone in the system is just using that much more water. When we got all the readings in for this term it was quite a bit higher than the last one. So either someone has a break on their end (past the meter) or a farm or business is just using that much more. Once we go over all the numbers we should be able to pinpoint where its going. Either way we can now breath a little easier knowing there isn't some huge break out there. Thanks for all the ideas, may still come in useful at some point.