The cache is not at the listed co-ordinates but parking is nearby.
Greater Sydney's water network has many dams and reservoirs forming the network. The great benefit of an interconnected network is the ability to substitute water sources. The image below courtesy of Sydney Water shows how the Greater Sydney network is setup. This of course is supplemented by further downstream reservoirs with interconnecting trunk mains around Sydney.

The cache can be found at;

Chmmyr; Vgf nyy gurer. Sbhe sbhe yrggre jbeqf. Qnzf glcvpnyyl qba'g unir xrlf nf bcravat gur qbbef vf abg n tbbq guvat.
TM 750. Fgnl Qel. Nagv TBZ Pbagnvare