Water damage in the basement still during construction - what to do?

Then it’s not your problem at all, but the general contractor’s.... Or did you outsource partial trades and now the GC wants to claim that someone else messed up?

No, everything was built by the GC. But they are trying to talk their way out of it: a dehumidifier was standing nearby with the drain hose in a bucket about a week ago – the water had spilled out of the bucket.