I had half a bag left over from last year. I used it this year and didn't have to add any water.
I do remember reading reviews when it first came out about people having issues with it drying out. However, I could never tell if it was due to the product, or operator error. I think a lot of it was newbie paranoia...OMG my eggs are deflating!!! <<< How many threads like that pop up only to find the eggs are a week away from hatching and are just fine. Some of the other complaints came from people breeding lizards or something that requires a different moisture content than Balls. Could have also just been a production problem early on that has since been sorted out.
I don't know...all I know is it works for me.