Well most of the times it could be due to faulty or inefficient piping and drainage in building while construction, this problem takes time to completely go away. Use Roff Hyseal, it is a waterproof coating.
Process –
1. Clean the walls completely
2. 2. get rid of all the flaking and everything
3. 3. Apply Hyseal on a clean wet surface
Keep curing it with water for a week this is what helps for lasting effect. I followed this and it has been comparatively better than the other waterproofing products I used. Hope this help you too.