PAPond, after I posted, I realized how painfully obvious my reply was to your question. Apologies.

I'm still not sure what you are trying to do though. Are you just trying to know how much water you transferred from the first pond to the second?

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."