Maria O' Brien died after she was attacked on the grounds at St Otterans psychiatric hospital in the city.
A 36 year old man charged following the fatal stabbing on Friday evening was detained at Waterford Garda station overnight and will appear in court later today.
55 year old Maria O' Brien died after she was attacked at around 7pm on the grounds of St Otterans, where she was a patient.
Another patient and staff member were also injured, they're being treated for non-life threatening injuries.
A post mortem was carried out on Ms O' Brien's body yesterday at University Hospital Waterford.
Both the Gardai and the HSE are carrying out separate investigations.
The 36 year old man charged, was also a patient at St Otterans.
He'll appear before a special sitting of Waterford District Court later today.
