jclaiborne already answered your question on page 1.
Without proper humidity in the enclosure, supplemental hydration is a waste of time - the animal is losing moisture through every breath. They need moisture in the air to stay properly hydrated.
While i don't rescue varanids anymore, when I did, I never gave them supplemental hydration. They went straight into a stock tank with a 2' deep damp, diggable substrate. I made sure the humidity was correct and that the hot spot was properly hot. I did not even look at the animal for a week.
Dehydration in varanids leads to gout and it's a slow, process. That baby you rescued probably had a host of issues too boot - internal parasites, stress, dehydration.
Handling reptiles induces stress and stress negatively impacts the immune system - which will put an already sick animal a foot further into the grave. Giving the animal chance means eliminating stressors.