I wasn't criticising you actually, but I used to think it was OK to feed my cats whatever was cheapest in the supermarket, with no thought as to ingredients. Thanks to forums, I know better, so do share my knowledge as that is the main point of forums - and yes, my vet has also asked me for advice on cats, esp on the behaviour side. I had an overweight foster with cystitis - one vet recommended dry c/d, he got cystitis while on it, so I took him to another vet, they gave wet food only and cystaid - and he rarely suffered. Both professionals, and both with years of experience. My vet knows I do my research though and will question her if I am unsure as it is different to what I have read - and I do stump her with health issues on a regular basis!!
I haven't heard about too much water affecting their liver - although cats with liver problems do drink more than 'healthy' cats, and my vet gave sub-q fluids to my cat with liver probs. Too little water can affect their health though.