I think that would depend on if things stay static as far as the up-pond spring flow, and if that flow would match, exceed, or be less than potential leakage of the spring in the pond basin.

Why do you think you're going to miss lining a potential stream? Are you not lining the entire pond basin?

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."