The BBC has learned that NI Water is being investigated by the Information Commissioner over its compliance with the Freedom of Information Act.
The commissioner's office has said it will not give details of the probe, which began in July, in case it prejudices its investigation.
A spokesperson for NI Water said it would not comment on the probe.
Its board is meeting next week to discuss recent media coverage of the controversy surrounding the company.
Northern Ireland Water has been in the spotlight in recent months, following the sacking of four of its directors and an investigation by the assembly's public accounts committee (PAC).
The committee probed not just the sackings but also Northern Ireland Water's failure to ensure competition when handing out contracts.
On Tuesday, the most senior civil servant in the Department of Regional Development, Paul Priestly, was suspended pending an investigation into the events surrounding NI Water and a related investigation by the PAC.
The civil service said his suspension was to facilitate the probe and was not a disciplinary penalty.
On Thursday, Regional Development Minister Conor Murphy backed the decision to suspend Mr Priestly.
Mr Murphy spoke about a phone call he had with Mr Priestly on Tuesday when new details emerged.
Mr Murphy did not give specific details about his phone call, but suggested the suspension related to the Public Accounts Committee's NI Water probe.