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Details:
Pumps Don't pump water Into Fluid Wagons
I'm on a Mac
Mods used:
Texugo Wind Generator
Deep Core Mining
Upgrade And Building Planner

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At most three pumps can connect to any tank car. On the right side, you do have three pumps connected to each rail car.
It's not working on the left side, though. Pumps are incredibly picky about where the tank car is sitting. As I understand it, putting a curve between the station and the pumps basically means that the pumps won't connect.

Two other notes:
Because Factorio-fluid-mechanics, you're much better off if your pumps connect directly from a tank to the rail-car, with no intervening pipes.
I see you have a section for barrel manufacturing. Have you considered using barrels instead? Your capacity will go down (20k/wagon instead of 25k/wagon), and you'll have to add a bunch of assembly machines, but you can use inserters, which will be perfectly happy with those wagon positions.

Pumps have very fragile hitboxes. Make sure the train is perfectly straight or it might not connect.