5.5 Patch Notes, Zac W changes clarification

I realize the patch notes literally just went out, but I was hoping for some more clarification on what exactly the changes for Zac's W mean.

When you say "reservoir" do you mean that if Zac's W isn't on CD but he picks up a chunk, the CDR reduction will stick and apply when he does cast it?

Maybe I'm just not reading it correctly and I'm being stupid, but could you clarify on it?

Can I just say that these patch notes look fantastic? I'm always excited for Zac and Volibear changes and the new jungle item looks great.