Some possible solutions: 1) Desalinate sea water and pump it up to Lake Gatun. 2) Build catch basins next to each lock that can take half the water from each

Some possible solutions: 1) Desalinate sea water and pump it up to Lake Gatun. 2) Build catch basins next to each lock that can take half the water from each lock when the level is being lowered and can then give it back to the lock when the level is being raised. 3) Lower blocks of shipping containers that are heavier than the water they displace into a lock to occupy any space a ship does not occupy. Less water will then be needed to operate the lock.