The reference in % is always the total weight of the flour. For the result, we consider 100% levain hydration. That is, equal parts of flour and water.
Why is bread hydration important?
The hydration level of your bread will impact certain factors such as
texture, crumb and shape.
A less hydrated dough means a less sticky dough, but it will be more difficult to incorporate the ingredients. Gluten will take longer to develop and fermentation will take longer.
A more hydrated dough means you will have a sticky
dough, making it harder to shape. The ingredients will be incorporated
more easily and the biggest point of attention is the fermentation time.
The more water your bread has, the faster it will ferment, so be careful
not to over-ferment your bread.