Re-Waterproofing a Leaky Basement

Re-waterproofing the outside of a basement wall requires excavation to the full depth of the wall, careful cleaning of the wall surface and proper application of bituminous waterproofing.
A multi-layered membrane system should be used if the surrounding water conditions are severe. At the same time, a perimeter drain system should be installed, similar to the recommendations noted above for a new foundation.
If there are cracks in a wall, the cracks should be chipped out to form a V-groove along the length of the crack approximately one inch deep. The V-groove should then be sealed with a good quality epoxy or silicone caulking, filled with mortar and covered with bituminous waterproofing.
An effective, but sometimes expensive alternative is epoxy injection into the crack. This can be done from the inside.
The epoxy bonds with the concrete and creates a somewhat permanent seal against water penetration. The limitations to this system are cost and effectiveness, depending on the size of the crack. The smaller the crack, the less likely it is that full penetration injection is possible.
However, before undertaking expensive excavation around the outside of a foundation, you may want to get proposals from local epoxy companies to compare the cost and potential effectiveness.
Waterproofing that is claimed to be effective by injecting into the soil on the outside of the foundation is almost always unsuccessful.
Any attempt at sealing the outside of a foundation by injecting any material through the soil is time proven to be unreliable.
Basement water is controllable but there is no easy answer. Only the more complex and sometimes expensive approaches are truly reliable.