Is mineral or spring water okay for my cat?

Yes, for most cats. The small amount of minerals in spring or mineral water is not a meaningful health factor for a healthy indoor cat, and what actually matters is that the water is fresh, clean and available in a spot your cat will use. The one exception is a cat with a history of urinary crystals or bladder stones, where a vet may want to control mineral intake more closely, including in water. If your cat has no urinary history, tap, filtered or bottled water are all fine choices; pick whichever one gets her drinking consistently.