The water analogy is great for generally explaining voltage and current. The thing that is missing is heat produced by current flow in electrical circuits.
Wiring is sized for the load in amps as defined in the National Electrical Code and protected by a circuit breaker or fuse. A circuit breakers only function is too prevent fire.
Generally
15A - #14AWG
20A - #12AWG
30A - #10AWG
50A - #6AWG
One can get away connecting a #10 AWG cord to a 50 Amp CB 99.9% of the time. Just know that a problem between your RV disruption panel main CB and the RV Park connection will not be properly protected.
Hugh
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