I am always curious when people talk about kidney and bladder problems why water is not brought up. Much of the concerns can be traced back to water. For all my pets I have changed over to distillied water because in my area the water is quite hard.
Food is definitely a contributor to concerns and foods that are high in fibre are going to draw water from the body. For cats I have read that a good way to get them to drink is to have multiple water sources and move them around.
The talk regarding corn in performatrin is confusing two different types of performatrin. The basic line has corn and the ultra does not.
Another ingredient I like in a cat food is cranberry which has the same benefits as for people which is that it prevents things adhering to the bladder and urinary tract walls. Still all in all I think the main concern should be the quality of water and amount of water.