Can you tell me how are kidney stones a deviation from homeostasis?

Kidney stones: Kidney stones form due to supersaturation of minerals, stasis (lack of flow) of urine or infection. Think of it like pouring salt into a glass of water - once you pour in too much salt, it begins to come out of solution and precipitate at the bottom of the glass. So it is with stones - too much calcium, oxalate, etc or too little water (urine) can cause stones to precipitate in the urine.