The utility says there has been no breach of its security systems
Irish Water says some its customers are being targeted by a phishing scam.
It says some people have received e-mails purporting to be from Irish Water with the subject line 'Your Irish Water Account - Action required'.
The utility is advising anyone who receives these e-mails to delete them immediately.
In a statement, the company says: "Irish Water will never ask customers to update personal banking information in this way and customers should always delete e-mails requesting this information.
"Do not reply or click on the link provided. Do not provide personal or financial details."
Irish Water says it has investigated the issue and has requested that this fraudulent site be shut down.
It says attempts may be made to deceive customers with phishing e-mails during the refund process in particular.
The company says it has put additional resources in place to try and guard against these phishing campaigns.
Irish Water says there has been no breach of its security systems and that customer details on its database are secure "and have not been compromised."
Anyone who suspects they may have responded to a phishing e-mail is advised to take the following steps: