There are some pleasant and very quiet backroads behind Gloucester, leading into the Barrington Tops area. Wooden decked bridges are frequent , and can be slightly hazardous, especially for thin tyres - approach these bridges cautiously. The longest stretches without access to drinking water would be around 20 km or less. Tap water is theoretically safe to drink in all places. If possible, however, try to find rain water, which is collected in metal or plastic tanks and usually more palatable - farmsteads will usually be happy to provide drinking water.
Bottled water is readily available in large supermarkets.
Ground water will not be safe anywhere. Supermarkets often have liquor stores attached. Be sure to bury all toilet waste carefully. In many places there is enough wood for a small pit fire, and you can cook or make damper easily. Use wood sparingly and observe all fire precautions and bans.