Water CAN BE pumped.
Why would you pump water if there’s plenty of it at the height of Lake Gatun. Hence, no pumps were built back in the day because there was plenty of water.
But, the demand for transit has increased tremendously. Ships loiter waiting transit. These wait times are costly.
To be sure, pumping water - if pumping water is feasible - will probably impact fees for transit. Such are the realities of the world.
Now, let’s ask the question: why are there any deserts in the world? Because the cost of pumping water, and desalinization where necessary, isn’t free.
You are correct, 100 years plus later and the capacity cannot meet the expanded design to meet the increase need— all true.
Your post reminded of the water that is in aquifers under the desert in africa, and in Saudi Arabia- being tapped iirc.