Because watercolor actually moves on the paper, it is the most active of all mediums, almost a performance art.
I equate inspiration with desire the desire that moves us to be artists in the first place. To attempt to make a painting without this motivation is a waste of time.
Gather and hoard your inspirations as you live, then recapture them as needed in the studio.
Anyone who tries to make a living as a painter knows you can't lounge about waiting for inspiration to hit; nothing motivates like keeping a roof over your head.