Why aren't they reusing the fresh water from the locks? Sounds like that when they empty a lock, they're just dumping the water and then refilling the next time from Gatun Lake.
Just pump the water back into the lake and use it again.
Pump? With WHAT?
The whole point of a gravity driven canal lock system is that YOU DON'T NEED PUMPS. They work spectacularly well when idiots don't run them beyond capacity.