This is a very nice clear description of how to protect the health of your pet’s bladder, and of the causes and prevention of stones and crystals in the bladder.

I found it on one of my favorite sites, and she made the excellent additional point that in the case of cats, it’s also very important that they get extra moisture in their diets, as they have evolved to get most of their moisture from the prey they eat.  They generally don’t drink enough to offset the fact that their primary diet is often dry, putting their kidneys in a mild state of dehydration for years at a time. Combined with feeding a diet high in carbs, it’s no wonder why bladder and kidney problems are so prevalent for cats.

See these links to read more about these issues in cats (though the info is useful for dog owners as well):

A good explanation of why cats on dry diets need more moisture (this whole page is good actually, not just this section)

Tips for getting your cat to drink more water