Why does my car need a water pump with the timing belt? We always encourage those who have a timing belt to do the water pump at the same time, this is because in order to do your water pump you have to take off the timing belt to get to it. Really it makes good sense. I know there are more technical reasons and I could go ask Jason and he could give you all the explanations. I just don't want to charge you twice for the same job when I could have just done it all at the same time and saved you quite a bit of money.