Check the gap between the nahani trap and bathroom floor and fill it properly with cement.
Check all floor tile joints. Refill the opened joints with cement slurry.
Check the leakage drain pipe/release pipe for its proper working. Clean, if it is choked.
Check all the concealed pipes under flooring, like the basin drainpipes, for their water tightness. This can be checked by stopping the operation of wash hand basin and keeping these lines completely dry and operating them again after 4-5 days. If the leakages dry out and start, the source is through these lines. Break open the lines and locate the source and replace the affected part.
Check all the concealed pipe lines, as stated above.
If leakages still persist, try socketing and grouting of cement slurry in the affected portion.
Finally break open the bathroom waterproofing and re-do it carefully.
