For customers experiencing any issues with their NBN service, we recommend the best thing to do first is check if there's an outage on the NBN network.
We have created this article that can guide you on How to Check for NBN Network Outage
If there are no known outages in your area, customers can proceed with the troubleshooting steps indicated on this link : https://www.tpg.com.au/support/nbn-fttc/problems_connect_internet_nbn_fttc
In your case, sine the NBN connection box was submersed in water, we really need to replace it. We have sent an NBN technician who replaced the equipment and your connection should be working now.
Let us know should you need further assistance.