I agree with growler's comments about discussing it with your vet and that individual cats may have different requirements for fluids. One of my vet's guidelines is to consider fluids if the cat starts losing weight (which can indicate dehydration and loss of appetite).
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler