Hadn't heard about the corn liter going toxic. That is new to me. I do carefully get rid of all the pee spots, even tiny ones. So the liter should be quite dry. I've been using it for years to no ill effect.
I have only one cat and even so I completely empty the tray and clean and dry and put fresh liter in, once a month. The rest of the time i refill as needed.
Was using clumping clay for years. And there is a lot of clay dust in the house, which i probably breathed as well. Used the pellets from old newspapers, used pine pellets (they don't clump as well, just reduce to fine dust). And so far, the liter from corn is the best performing all around.
As for water. Yes they say it's best to never even give dry food. Cans or the raw diet is the way.
My cat won't eat anything else PERIOD, other then dry food. And he is specific as to what brand.
But luckily I have been taking to adding a bit of water to each of his meals (he gets 3 scoops divided into something like ten mini meals). So this way he is actually drinking about a cup of water a day.
Which is good. He was drinking quite a lot from his bowl anyway. But this is one way to make sure he is drinking a lot of water.
He won't eat canned food, but adding a bit of water to his dry food at each feeding seems to work.