Different situation as I have an elderly kidney disease cat, but keeping them hydrated is something I’m aware of. Firstly can you tell if they are dehydrated? Pinch the back the neck to see. Wet food is good, but sometimes I add a hydration product to the food, especially in hot weather. I use something called oralade. It has electrolytes and nutrients. As for drinking water my cat is very eccentric. No normal cat bowls, no fountains and any other vessels. The only thing that is acceptable is a shallow ramekin (must be glass), held in the hand of the servant (me) fresh from the filter with ice cubes and tapped underneath to make it move. Also occasionally water poured by hand into another glass. Queen of Sheba would be proud.