You pay for what the meter indicates, so if there was a leak before the meter, it would normally be the supplier's problem, not yours (except for the swamp it might create). When nobody is using any water, is the meter moving? If so, try turning off the shutoffs for various things: toilets, sinks, washing machine, etc. Have someone monitor the meter. If anyone of those stop the meter from moving, you've isolated the faulty item. As noted way back, the typical culprits are toilets. If you take th elide off the toilet(s), is the water up to the overflow? Or, if you shut the water off, does the tank water level drop overnight? Either of those point to a toilet using water when it shouldn't. Unless the house is floating on all of the water running, that water needs to be going down the drain. That limits it to things that have their own drain, like a toilet. If your sinks or shower were leaking, you'd probably notice it. Some whole-house humidifiers have a drain line for overflow, and that could be running all of the time as well. If you have floor drains, sometimes the put in trap primers...this dumps some water to keep the trap from drying out and allowing sewer gasses into the house. If one of those failed, it could be running and you may not see it, but often might hear it. It certainly would show up in the meter moving! Some logic and close inspection should find the problem. If you've exhausted all of the visible items, IF the pipes run under the slab after going through the meter, it could be leaking under the house somewhere. That would be harder to pinpoint, but fixing would normally involve either breaking up the floor, or redoing the piping so it is above ground. Does the WH run a lot? It could be a leak in the hot water line. This might show up as some area that is warm that wasn't before.
None of this is magic. Finding the problem should be straightforward. Fixing it, might be easy, or it may be difficult. Some things, like a leaking toilet flapper valve is within the capabilities of probably 90% of homeowners. Some others, can take more skill and tools. the least expensive option is to isolate the problem, then decide. It might take a plumber less time, but unless you get paid more than he does, it's worth it to find the problem yourself. Whether you can fix it or not is another question.