Faulty tanking - can it be repaired - a pump wasn't built in originally

Installing a sump and then a sump pump maybe an answer to the problem.

In principal; the cellar should have a means of draining excess ground water. Specification and scope is determined by stated application of use by the home owner. This depends on the type of tanking, the nature of damp and rate of rising ground water and it's potential to flood. There are minimum requirements for tanking cellars dependant on use and relevant BS standards that apply. Sounds to me that design and implementation is an issue here with this cellar tanking, as such any form of repair may not prove viable or economical to undertake and further guarantee. Mike Cobalt Carbon Free

The best thing all round would be To make a sump and fit a Pump that empty’s when required . There are many ways to try and fix the problem but if water is beginning to pool then a pump is the answer . Good luck

It depends what type of waterproofing system you mean when you say 'tanking'? A cementitious slurry such as Vandex is generally called tanking and this type of system does not need a pump. A membrane system (looks like bubble wrap on the walls and the floor) will need a pump OR drainage to a suitable outlet. If it is the second system then it doesn't need a pump if it is being drained under gravity, usually if only below ground on 2 or 3 walls of the room. Your problem might be that the drainage channels are blocked and need jetting or rodding clear.