Hair loss is another sign of detox. Often skin is the greatest place of toxin release.
I find the lower you get your toxin levels in your body the better your hair will look, and often it will grow back fuller and without grays.
If your scalp is one place your toxins like to release themselves there is very little you can do to prevent this. Your hair changes internally.
I suggest you continue your Water Fast until you know you have eliminated most of your toxins in your body. Over time your new hair will grow back healthier.
I find Water Fasting is a long journey, and it can take years to really repair the damage that has been caused by the toxins. I know if you persist and keep up the good work of fasting your body will start to show signs of improvement.