Who will bear the responsibility for flooding downstairs caused by the staggered sluice of the new house property?

If there is evidence that "before the renovation, you must apply to the property for opening the gate outside", but now it is because of the wrong operation of the property that the gate is opened, then the responsibility should ultimately be borne by the property in whole or in part.

But for the owners downstairs, there are still claims against you and the property. After all, it has something to do with your tap not being turned off. If the downstairs owner claims from you and causes you to take responsibility, you can recover from the property again.