covered by owner

Any repairs towards the property normal wear and tear and due to no fault of the tenant is under the responsibility of the landlord.

Under one of the TA clause, the tenant is to enjoy quiet enjoyment of the premise without any disturbance from the landlord or agent if rental payment is prompt.

Your landlord had therefore breached the TA. As the tenant, you can inform and forward all mails to the landlord for his further action.

Meanwhile, to expedite the matter, you can withhold further rental payment until the matter is resolve.

That is all you can do and is up to him to follow up with the apartment management.
If the water supply is with the Water Authority,  the apartment management have no legal authority to disconnect the water supply.

In a contract, the breached party must be given time to rectify the breach. Only if he fails, then the injured party can terminate the TA and claim whatever losses suffered.

In other words, if the water supply is indeed disconnected, you have to nego with the landlord how he intend to solve the problem. Only if there is no action from him then you can proceed to terminate the contract.

In a contract that is basically how it works.

For example, if the tenant default 1 month on rental payment, the landlord cannot come tomorrow to retake possession of the property. The landlord have to issue notices to the tenant to make good the rental.

Even if he intend to take possession, he has to go through the legal way. I am not going to discuss the illegal way since is not the topic.

As long there is no disconnection, the tenant has not suffer any losses. One cannot predict future problems or losses to terminate the contract, unless if can prove is life threatening.

Any legal actions relating to the property is between the management and landlord, unless the tenant is part of the problem.

Since the owner is not answering calls from the management, the only way is through you being the tenant. You can tell them that you have forward all things to the landlord and can ignore any further dealing with them.

Firstly, you didnt answer the following ....
How can the management and security didnt know the unit is tenanted. That shows that nobody knows what is going on until someone complaints.

Maybe the management just take the landlord's word and turn off the main to prevent further leak with no intention of making inconveniences to the tenant.

But  but, but then ....when the the problem first surfaced, I am sure someone from the lower unit would have approach you. No ?

the leaking could be costs by few factor, i.e. piping or water proofing or others

so better the owner go and engage his own contractor to check and do it

best advice is to look for the new unit as what the owner showed is he is not kind of responsive and responsibly people...

The landlord cannot stop you if you decide to move out. Just as I have explained in earlier posts, make sure you can catch him by his balls that he has breached the TA.

Wear and tear is part of rental agreement and the repair to be done by landlord.

If landlord refuses to take action, I would say a small leak wont cost a bomb in the bill.
If it is my own property, I will remove the tap, clean and roll over some teflon tape to stop the leak. If the leak is at the hose area, change it ....not expensive. Available at MrDiy.