Where your responsibility starts
Two separate lines run between your building and the street. The water service brings potable water from the city main to the meter, typically 3/4 inch copper on anything modern. The sanitary lateral carries everything from the building drain out to the city sewer. They fail in different ways and they are repaired in different ways, and only one of them tends to give you notice.
In Toronto the split falls at the property line. The city looks after the public portion between its main and that line, and the owner is responsible for everything from there into the building. The boundary does not correspond to anything visible in your yard, which is why the first useful step is a locate rather than a shovel. Other GTA municipalities draw it in broadly similar places, but the details differ and are worth confirming before you commit to work.
Older housing adds a wrinkle. Water services in houses built before the mid-1950s are often lead, and frequently only part of the run has been replaced: the public side swapped at some point, the private side left original. The city has run a program covering the public portion. The private side stays with the owner, and replacing half of a lead service is not the improvement it sounds like.