The first year, our consumption averaged 2300 'units' per month. Two months ago, usage jumped to 39,000 units so I cut off water to toilet that seemed to run constantly. Last month's bill did drop but only to 29,000 units. What could be the problem since there are no obvious leaks in or out of the condo? Meter defect?

There is a leak test dial on a water meter that can determine that there is consumption.

Toilets. Put food coloring in the tank and see if it appears in the bowl.

Fluidmaster now makes a flush valve that will protect against toilet leaks.

As for the toilet problem - the flapper is not sealing.

Please note that the usage was typically about 26 hundred 'units' and skyrocketed to 39 thousand units, then by cutting off the running toilet, it dropped to 29 thousand. Still 10 times normal!

Check multiple toilets if you have them.

Look at the leak detect dial on the water meter.

Another possibility is the washer and the water heater T & P valve.

The hot water heater temperature and pressure relief valve is always a good suspect.