The floor should be at least 4" thick. Doubtful that the Water Department will fix a leak you caused, without charging you. Most times, the water line from the City tap to your home is your problem, even if it is before the meter. They usually consider any pipe from the curb stop at the property line, yours. With the home being only six months old, I would be contacting the builder. The City should also have inspected the concrete job.