Looks like another major expense heading our way. HDB came over to inspect our bathroom to determine the source of our downstairs neighbour's roof leakage. Assessment: We're going to need a whole new bathroom. Floor tiles out, crapper out, and while we're at it, wall tiles out, bathroom sink out -- hey, and maybe get a replacement water heater too!
It's likely that it was our darned air-con contractor's fault in the first place, giving us an a/c drainage pipe that drained impractically into the drainage hole of our main bathroom floor instead of the shower hole. Because the drainage hole was at the far end of our bathroom, the contractor ran a long PVC pipe all the way across our bathroom floor which became a tripping hazard for us. June got fed up with the pipe one day and had it hacksawed off. So the a/c drained directly onto the bathroom floor. The water must have eroded the sealant between our bathroom tiles and thus started seeping into the floor below. Hence, new waterproof lining has to be installed, and hence, our new bathroom (minimalist in design due to budgetary constraints) will rise from the rubble of the old.
Um... in case there is anyone out there who is looking for evidence indicating whose fault is the greater, the above raises mere speculation on my part and does in no part constitute a confession.
What happens now? An HDB contractor will be engaged who will bring steely tools and beefy men to tear up our bathroom fixtures and install new ones with more gusto than finesse; and will gleefully send us a huge, hefty bill at the end of it all. How we then proceed with the apportioning of the bill between the parties involved will be another story for another time.