The site, on council land, on the corner of Southampton St East and Hastings St South, would also include a reservoir roughly up to 38m diameter and 15m tall, together with associated pumps, filtration, chlorination and UV infrastructure housed in a purpose-built building (of approximately 200sq m in size and up to 8m tall).
The investigation will be conducted by Palmerston North lawyer Alastair Hall and is to establish, if possible, whether there was an "improper disclosure" of Water Central details and councillor only sessions on September 26 and 27, and if so who was the source of that disclosure.
It will cover council staff, contractors, and elected members.
In a letter to the editor, published on Tuesday, councillors Rod Heaps, Simon Nixon and Malcolm Dixon labelled the investigation an "absolute waste of money".
They said their "guesstimate" of an $100,000 cost may be on the low side when staff time is taken into consideration.