Certainly the additional set of parallel locks opened in recent years would only serve to hasten the speed with which they are dumping the fresh water into the oceans on each side.
This article from 2003 talked about two-way traffic on the canal: https://pancanal.com/en/panama-canal-begins-tests-of-simulta...
- On the new locks they recycle ~60% of the water used already, it's a smart system.
- Another commenter pointed out that they have to allow fresh water through the lock system to prevent salt water contamination of the lakes.
I guess a reason they haven't retro-fitted (yet) the 60% water saving mechanism to the older locks is the scale of the engineering efford involved, plus they can charge people $4.5 million to jump the queue ;)
Also, anything taking the old locks out of operation for a few weeks/months is basically a no-go. That's just too costly.
As a side note, do keep in mind that water is already "saved" a little by going up in a convoy. With the three lock chambers, you get to reuse the same water three times. Not exactly true of course because convoys start and end, but you get the idea.