Who pays for water usage for a leakage? NSW

new tenant sep 2014
Sent first water bill about Jan 2015, approx $400 which is on the high side,
a month later, I follow up with the agent and they say, oops we got it but we couldnt read the scan (I was like well you should have called me, because the attachement is fine, as others can read it), oh ok, we will pass it on

fast fwd to today, bill of $5000,
obviously a leak of some sort,

who pays for the usage, even the agent werent 100% sure
In S.A. an I get an allowance if the pipes on my property have been leaking?
SA Water may provide you with an allowance if you discover that you have had a concealed leak in your private pipe work. The allowance, equal to 50% of the deemed water wasted, may be granted if certain conditions are met. Allowances are capped at 300kL. SA Water will give only one allowance in a ten year period of a property continuing in the same ownership. Leaks must be repaired by the customer within six weeks of detection, or the printing date shown on the Notice of High Water Use.

At 5 litres a minute,thats some leak you must have!!
In Qld one our IP had pipe leak underground between meter and IP. High water meter reading tipped off something wrong. Long story short after leak was identified an repaired, water company wiped the bill off.
That's a massive bill. Normally you get a plumber out and then they complete the plumbers statement form for Sydney water.
In this case you should speak to Sydney water to find out what they can do because this is a large amount and has been over a long period..

With regards to who has to pay. It will most likely be you if Sydney water doesn't cancel it.
The tenant wouldn't have been aware of any issues and due to the leak being the cause of the increased usage, the tenant wouldn't be required to pay any extra amount than normal usage.

Also, by the looks of it, the agent didn't forward the copy of the bill to the tenant and therefore the tenant didn't know of the increased usage either for a period of time. It would have been ideal for the property manager to actually open the bill and pass it onto the tenant first of all and also ask about their usage patterns because $400 is a lot for usage. If the usage seems fair then it would have been dismissed, but if not then they should have organised for a plumber to investigate. Maintenance and repairs are the owners responsibility after all.