Management at Turoa skifield was told diesel was missing from a tank three days before the leak was made public, according to a worker.
About 19,000 litres of diesel spilled from the tank, behind the Turoa ski lodge, on September 27 and leached into the Makotuku Stream, contaminating Raetihi's water supply.
An employee of Ruapehu Alpine Lifts (RAL) at Turoa, who spoke to the Chronicle on condition of anonymity, said diesel from the 40,000-litre storage tank was being moved to smaller tanks at the top of the lifts on the night of September 26/27.
"During the day my supervisor contacted me to ask how much was in the tank before we started transferring.
"There was 22,000 litres and we transferred 3000 litres, so it was then known that 19,000 was missing.
"My supervisor informed the ski area manager of the figure but nothing was done, [and he] was told by maintenance that a substantial amount of diesel had leaked, but no action was taken.
"I know this was communicated through to Chris Thrupp, the Turoa [operations] manager, by a number of different staff members on Friday the 27th."
The worker claims that the Raetihi water crisis could have been avoided if the company had come clean sooner.
"What is happening to the poor people of Raetihi could have been prevented."
Mr Thrupp said he was unable to comment as he didn't want to prejudice the inquiry into the spill.
He said such incidents were "often judged with hindsight, which was not available to staff at the time".
Dave Mazey, chief executive of RAL, said he was unaware of any communications to Mr Thrupp about the tank on September 27. He was unhappy a staff member had contacted the media.
"I would appreciate knowing who that employee was so I can read them the media clause in our contract."
Mr Mazey previously told the Chronicle it wasn't until October 1 or 2 that staff "dipped" the tank and discovered its contents were much lower than expected.
In the interview last week, Mr Mazey said two pipes connecting the storage tank to two bowser pumps separated during the night of September 26/27, causing the spill.