you can use water to bleed them, the only problem with water is that it slowly degrades the oil seals in the brake, if you use a small amount of anti freeze in the mix it will make the seals last longer, and stop the water freezing in the winter, you should be careful when using other thinner types of oil, make sure the oil you are using is mineral based, any other oil such as dot 4 or 5.1 will destroy the seals,