The primary water supply for Palmerston North is taken from the catchment area of the Turitea Stream at the northern end of the Tararua Ranges. The catchment has an area of approximately 2,400 hectares which is largely covered in bush. The average rainfall is 1,400 mm per year. (Description from PNCC)
For more information on the water treatment plant, see this pdf (500kb) detailing its history (from PNCC website).
The cache is a 200ml Sistema container with a log book, pencil and a few items.
Note: The GPS jumps around a bit near GZ, but you do not need to cross any fences or climb down or up any cliffs to find this cache. It should be a quick find for geocachers. Also the cache is near an open stream so those with kids should take care.
Please return the cache to the same spot you found it, and make sure it is out of sight from the road :)