While a plan has been put in place to temporarily rehome patients at Knockbracken Healthcare Park south of Belfast, that facility has not been used to date.
The trust is taking legal advice over where liability for the building failures lies.
The facility was built by Graham BAM Healthcare Partnership (GBHP), a joint partnership between County Down-based Graham Construction and BAM Ireland in the Republic of Ireland.
GBHP has also been involved in Belfast’s new maternity hospital which remains unopened and almost £50m over budget.
The Belfast Trust said it was “currently working with its legal advisors to appoint independent specialists to undertake a comprehensive review of the water system and any potential sources of water ingress and to help identify liability for the costs of the remediation work”.
In a response to the BBC, the trust said a survey of the entire building had taken place ahead of the repair works.
In August 2024, the body which inspects healthcare facilities – the RQIA – issued a notice to the trust telling it to replace doors and door handles at the facility because of potential patient self-harm as a result of ligature risks.
This was to be complied with by 17 February this year, with an extension granted to April, and now compliance required by this November.