Ruapehu District Council is continuing to test and adjust the hydrocarbon sensor on Raetihi's water intake in preparation for returning the Makotuku River as the township's water source.
The use of the sensor is a first for New Zealand.
A spill from the Turoa skifield on Mt Ruapehu in October last year leaked 19,000 litres of diesel into the Makotuku River forcing the council to switch the water source for Raetihi township to the Makara Stream.
Since civil defence response phase to the diesel spill ended, the council has been working to return Raetihi's water source to the Makotuku River.
Council environment manager Anne-Marie Westcott said that the successful installation of a hydrocarbon sensor on the raw water line feeding the Raetihi water treatment plant is a critical factor in enabling council to return the water supply to the Makotuku.