Strangely enough, our cats drink a lot of stale water - from buckets and lids in the garden, anywhere they can find it. They don't like it fresh from the tap.
However - 3 days? - no. Overnight, yes, but no longer. I would have sorted out the arrangements for the cats before I booked my holiday.
I see Jayne's not responded - Jayne - no neighbours who can look in on your cat? poor thing will be lonely and worried that you're not coming back....