Did he check meter flow per minute?  In other words when you use water is more water flowing through the meter than into your house?  I can't remember exactly how, but they measured the meter flow to the volume of water.  Discovered a deep leak in our pipe from the meter to the house.  Our neighbors leak was the same only his was under the road and ours was in our yard.

Good luck.

If they find a leak ask them to forgive the bill.  They would rather see it fixed than have an unusually high charge go for a customer.

Is it possible they misread the meter?  If it was real usage the water had to go somewhere.  Did they suggest putting a camera down the line to see if there is a break?

You can troubleshoot and fix anything. Have you read this? Do you have any suggestions?

Most of those have already been tried.

Step 1. Make sure you can actually check the meter yourself. Read it, and write down the number. Do this with the master valve on but all the faucets off.

Step 2. Listen carefully for the sound of water spurting anywhere. Watch the meter and see if it moves at all. If you have a leak then you'll absolutely notice the movement.

Step 3. If nothing is flowing, try a controlled test. Fill a bathtub or sink, or start a load of laundry. Re-read the meter and see if the new reading is roughly 30 to 50 gallons depending on tub or washing machine capacity.

Once the machine is agitating, the flow should stop again. It should start up again when it does the rinse cycle.

If this looks like normal usage, now we could look at someone else using water.

Start reading your meter at least twice a day. If you have all the faucets off for 12 hours, then it shouldn't move the needle at all.

Make sure the master valve isn't being confused as "off" when it's really "on" and vice versa. Check the non-working faucet with the master valve in the opposite position, just in case it is mistakenly confused on from off. I have seen seasoned plumbers make this kind of error, and I have also seen mis-marked valves before.

Check the meter again after each step. It can be tedious and seem to have a lot of unnecessary steps, but you want to be able to catch even uncommon problems.

The once every 12 hours meter read with all the faucets off can catch a pattern if someone is actually stealing water. Also check the meter immediately before and after doing any outdoor watering, to get a water consumption baseline of actual usage.

Do not leave sprinklers or other things running unattended. If you have sandy soil, tens of thousands of gallons of water can soak right in without making a huge puddle or small lake.

A friend of mine had a leak just past his meter a couple of years ago and ended up with a nearly $3,000 water bill. Seems a piece of heavy equipment had broken the plastic pipe, but the sandy soil soaked it all up without turning the terrain into a swamp. Once that was fixed, we installed a web cam to watch the meter and take a snapshot and save / email it every 3 hours.

If you notice any sudden unusual spikes in water usage over a 12 hour interval, you can narrow down the source of the problem far more quickly. If necessary, shut the master valve off to stop the flow again until you're actually probing for the leak.

You could also start checking it every 6 hours during that window of time where heavy usage appears. You might even do things like rake / plow the soil around all the outdoor faucets so anyone doing something they shouldn't will leave footprints and other signs of their presence.

Someone I knew who served in Vietnam would have likely taken some monofilament fishing line and rigged a couple of trip wires. Almost anything that will trigger a source of light and noise would work.

These days, a passive infrared motion activated camera / alarm system is nearly impossible to detect and defeat. A wildlife camera with night vision, carefully mounted with a good look at the suspect area will silently capture images or video of anything that enters its field of view, whether it's a 4 legged or 2 legged varmint.

Also if you shut the water off at the meter valve whenever you go to bed or go into town for shopping, you can also use some kind of tamper evident seal that someone can't fix completely - a piece of clear tape stuck to the valve actuator that will break when it is turned, would still be intact when you returned. If you use something distinctive that is hard to duplicate, then someone can't just put their own new tape in place if they get wise to the valve being shut off.

That's mostly what I can think of now.