$$\ce{HA(aq) +H2O(l) <=>H3O+(aq) +A- (aq)}$$
Say the acid solution is currently in equilibrium. How would diluting the acid by adding water change the equilibrium position? Le Chatelier's Principle says pure liquids like water do not affect the equilibrium position. Using the equilibrium constant, it is easy to show the reaction should shift towards the right, but how can we show that with Le Chatelier's Principle?