At approximately 10.30 pm, on 23 March 2004, a hose attachment was made between the process water and the clean water pipe system in the Ranger ore processing facility, near Kakadu National Park. Early the following day, workers showering after the night shift complained of skin irritation and poor quality drinking water. There were also reports of nausea, stomach cramps and vomiting from drinking contaminated water. Energy Resources Australia (ERA) admitted there were at least 28 workers that either drank or showered in water that had 400 times the legal dose of uranium.

Initial testing by ERA indicated that the water had a mild acidic ph of 4.5 and an elevated uranium content of eight parts per million. In response to this incident, ERA decided to close down both the clean water and process water systems, send non-essential staff home and conduct an orderly shutdown of the mine and all processing facilities.

A report by the Department of Environment and Heritage concluded that the primary cause of the contamination of the potable water system at the Ranger mine was that an operator opened a valve connecting the water manifold at the Fine Ore Bin (FOB) Scrubber to a one inch hose. At the time of this connection, the manifold was also connected to the process water system. Unknown to this operator, the other end of the one inch hose was connected to the potable water system and the valve at that end of the hose was open. The higher pressure in the process water system caused water to flow from the process water system into the potable water supply system.