BCA有这么一个假设原则的https://www1.bca.gov.sg/regulatory-info/building-maintenance-and-strata-management/management-corporation-strata-title-mcst/strata-living-guide
里面有下载的链接，参考正文第7页
不知道我有没有抓住重点
Inter-floor leaks
If there is an inter-floor leak, you and your neighbour are required to jointly carry
out an investigation to establish the cause of the leak and proceed with the repair
works. You should also both resolve the cost of repair. In cases like this, it is presumed that the leak has originated from the upper floor unit unless the owner can prove otherwise. Therefore, the owner of the upper floor unit cannot claim that
the leak has not originated from a defect in his unit. He has to jointly investigate the cause with his lower-floor neighbour and proceed with any repairs required.
If there is an inter-floor leak, you and your neighbour are required to jointly carry
out an investigation to establish the cause of the leak and proceed with the repair
works. You should also both resolve the cost of repair. In cases like this, it is presumed that the leak has originated from the upper floor unit unless the owner can prove otherwise. Therefore, the owner of the upper floor unit cannot claim that
the leak has not originated from a defect in his unit. He has to jointly investigate the cause with his lower-floor neighbour and proceed with any repairs required.
Huasing Association 1999 - 2013