Well, today my mother and I were giving my cat some water when we noticed patches of extremely thin and transparent hair on her front legs. She is a dark-gray tabby, thick hair, and slightly senile (9 years). She is fed Purina 1- salmon and tuna catfood and is given water from the refrigerator usually, ( water is twice filtered) although sometimes she gets water from the sink, (water is filtered only once)... we have well water, not tap. She does not go outside (or at least, not usually- sometimes she escapes) She uses Fresh Step litter, but she won't pee in the litterbox recently... she pees on towels, and in sinks. However, she poos in the litterbox regularly. One of my two cats threw up everywhere this morning... however, I haven't noticed any weight loss in Cuddles, the cat in question. She is no more lazy or listless than usual, or at least not noticably.... I haven't seen any signs of anal, optic, or nasal discharge.... the only real symptom I have are spots of very thinned hair on her legs. What could this be??