These water tanks were fed by a water intake in Skerretts Creek. Built in the 1950s, they were abandoned in the mid 1960s when the water catchment ceased operating. Some older residents including myself claim there were four or more water tanks originally, with two being completely destroyed over the years. Not far from these tanks is another site containing two additional tanks above the hill behind. They can be accessed via the nearby track to Crowther Trig.
Appendix
This 1969 photo below is evidence that there were actually four water tanks (perhaps five). You might need to zoom in to see them, but they are located to the left of the image. Click the image, go full screen, then use your device to zoom in. You can also see the two additional tanks on the track to Mount Crowther just above and to the right of the four or five tanks.
Image sourced from LINZ Data Service and is licensed for reuse under the CC BY 4.0 licence.