Great question! I'll be interested in what others think about this.
My view is that clean fresh water has no equal and cannot be improved upon. Some add ACV to it, but if you feed FF, this is a needless exercise.
Regarding the FF excess water, I feel the best thing to do about that is to adjust the ratio of dry feed to water to achieve a thicker consistency. I feed FF at the consistency of thick oatmeal, adding more dry crumble toward the end of the bucket as the mixture "sheds" water.
Here is my "recipe": To 24 cups (7 quarts) of water, I add 28 cups of dry feed.
I keep two buckets, starting a new batch in the second bucket as the first gets down to one day of feed-out remaining. I use a cup of the previous batch to jump start the new bucket so it ferments in just 24 hours. It needs to be at least 70F to achieve this quick fermentation.