I've been vegan for 4 months and I just noticed brittle nails but I'm not sure that my diet is the problem?

Florida has very hard water and it can really dry your skin out. I eat lots of veg and fruit as well, and still have dry skin/brittle nails. Having to use solvents at work, such as acetone and denatured alcohol, doesn't help matters either! Try rubbing in some Vitamin E oils from gelcaps directly onto your skin and nails. The moister you can keep the layers of keratin (hair, skin and nails), the less flaking that should occur.