I have a Flo-rite system to water my batteries ( 3 banks 8v Deep Cycle ) from one location. Flo-rite recommends adding water on a fully charged battery because you will lose some water during the charging cycle. Topping off water prior to charging and not after you might lose enough water during the charge cycle to be a problem.

In Actuality I top off water each time I open my generator compartment door.
I cycle which bank is used as the house bank and normally the last bank used will take a little water. A lot in the summer not so much in the winter.