The Supreme Court has found the ESB has liability for some flood damage caused to part of University College Cork's campus in 2009, overturning a decision of the Court of Appeal.
The court found the ESB was in breach of a duty of care to UCC during the floods in November 2009.
However, the issue of contributory negligence by UCC has yet to be dealt with and the case will also have to return to the High Court for damages to be assessed.
UCC had claimed the ESB's management of water releases from two hydroelectric dams on the River Lee led to significant, unnecessary additional flooding causing substantial damage to 29 buildings on its campus.
It brought the claim on behalf of its insurer Aviva.
The High Court found in 2015 that the ESB was 60% liable in respect of flooding and warnings. That decision was overturned by the Court of Appeal.
In its ruling, the Supreme Court found the ESB had a duty of care to landowners and occupiers downstream of the Lee dams.
It said the ESB had a "special and substantial" level of control that would enable it to prevent or reduce harm arising from a flood danger.
It also ruled the ESB had a duty to assess how a failure to increase the capacity of the Lee dams to absorb more of the anticipated storm flooding would affect those occupying land downstream.
It found the ESB had more than enough scientific expertise and knowledge to be able to assess the potential effects and should have had regard to the interests of those downstream land occupiers.
The court ruled that, in November 2009, this duty of care could have been complied with without placing a disproportionate burden on UCC or an impermissibly vague obligation on the ESB.
The court found no judgment call was made by the ESB about the proper course of action to take, which would have included the interests of those occupying land downstream.
It found that there did not appear to be any judgment call taken, which would have factored in any burden arising from altering the operation of the dams to give added protection to those downstream.
The case will have to return to the High Court for damages to be assessed.
The Supreme Court said that as a result of its decision, the only damages UCC was entitled to were damages representing the difference between the losses actually suffered by the university and those that would have been incurred anyway, if the Lee dams had not been operated in a negligent manner.
It said the High Court would have to decide how much of the damage could be linked to the negligence of the ESB.
The Supreme Court said the contributory negligence of UCC was still a "live issue" and would have to be determined at a further hearing of the Supreme Court but the assessment of damages could go ahead in the meantime.