The only way to stop him would be to file a lawsuit on an "emergent" (think "urgent" or "emergency") basis, seeking a court order requiring him to fix the leak or otherwise stop flooding you. Doing this is procedurally complex, especially if you are going for the fastest kind of court order, a "temporary restraining order" or "TRO"; you are strongly advised to retain an attorney to help you, rather than doing this yourself. In the course of this legal action, you can also seek monetary compensation for your costs, losses, and damages.