Answer: We don’t know where you reside so we will answer you question as if you live in Rhode Island (that is where our business resides). You are responsible for your water line starting at the curb and going all the way into your home so it doesn’t matter if it is city water.  Though detecting where the water leak is coming from could be a slightly helpful it really wouldn’t matter all that much because you would need to replace the whole water line anyway. The reason is because you never want to patch a water line leak only to have the problem again therefore having to dig up everything above the water line twice.  This would be a very expensive mistake.  When replacing the water line it should be one continues copper or plastic line depending on the local plumbing code.  If you want to determine if it is city water or ground water causing your flooding then we recommend you calling your local water department and have them shut off your water at the street to see if that stops your leak or not.  If it stops your leak then it is city water causing your problems and most likely your responsibility to fix however if it doesn’t stop your leak then it is ground water and you may need a larger sump pump or may be even two sump pumps.  Finally, we are not sure what your trying to ask in your second question but if your wondering if your sump pump is pumping the city water from your leak this is completely possible.