Why is it important to keep the temperature and the amount of water the same when testing surface area? Sample response: The temperature and the amount of water need to be kept the same so that the only variable that changes is surface area. If you allow the temperature and/or the amount of water to change too, you will not know which variable is causing the changes that you observe. Which of the following did you include in your answer? Check all that apply. The temperature and the amount of water need to be kept the same so that the only variable that changes is the surface area. If you allow the temperature and/or the amount of water to change too, you will not know which variable is causing the changes that you observe.