Height and branches
Water dragons perch, leap and climb. Thick horizontal branches at different heights, a basking branch under the lamps and a backdrop with ledges turn a tall box into usable territory.
The water area
Give a pool large enough to swim and fully submerge. A filter helps, but expect to clean often — they toilet in water. A drainable or removable tub saves your back.
Humidity without mould
Moderate-to-high humidity suits them, but stagnant air causes problems. Ventilate high and low, and use a substrate that holds some moisture without staying soggy.
Licensing
Native reptiles need a licence or permit in most Australian states and territories. Check your state wildlife authority before you buy.