The new set of locks in the Panama canal use "water-saving basins" to reduce the amount of water lost for each cycle of the locks. https://en.wikipedia.org/wiki

The new set of locks in the Panama canal use "water-saving basins" to reduce the amount of water lost for each cycle of the locks. https://en.wikipedia.org/wiki/Panama_Canal_expansion_project#Water-saving_basins https://en.wikipedia.org/wiki/Panama_Canal_expansion_project... I guess in principle something like this could also be retrofitted to the existing locks.