The first time I water fasted I was drinking about 5 liters a day, I had not been doing any salt loading and just been eating fruit for months, I was thirsty all the time.
I think salt is important to stay hydrated, if not you might end up drinking too much water, witch might give you pain in the kidneys.
I had bad kidney pain on the first fast, it didn't get much better and it wasn't until I completed another Water Fast of 14 days this pain went away. I think this might have been caused by too much water.
When it comes to drinking water on a water fasts, listen to your body and your own intuition, not just drink for the sake of drinking.