What to do iI maintanance came to my apartment to repair a leaky faucet but one of the water lines popped out after he was done and it flooded the entire apartment?

If there maintenance person caused the leak due some negligence (or carelessness) on his part, the complex would be liable as his employer. Or if the line ruptured due to either general inadequate maintenance (e.g. the pipes have gone too long between inspection and repair or replacement) or because of something else careless or negligent which the complex has done (for example, running the lines at too high a pressure; having installed pipes or lines inadquate for their purpose; etc.), the complex would again be liable for the damage. Only if it were the case that the complex had nothing to due with the rupture (e.g. you hit the line and broke it; there was a pressure surge in the municipal system which was not their responsibility; etc.) would they not be liable. Under the circumstance, it is most likely--but not certain--that the complex would be liable. Unfortunately, if the commplex will not voluntarily reimburse or compensate you, you'd have to sue them to recover the money. Depending on how much is involved, you could sue in small claims court and represent yourself, saving on legal fees. (For larger amounts, you would be better off retaining an attorney.) You could sue for the repair or replacement cost of the goods, and would have to show that it is more likely than not that the complex or its employees caused the damage.