https://en.wikipedia.org/wiki/Hydraulic_analogy#Limits_to_the_analogy

Charge: Unlike water, movable charge carriers can be positive or negative, and conductors can exhibit an overall positive or negative net charge. The mobile carriers in electric currents are usually electrons, but sometimes they are charged positively, such as the positive ions in an electrolyte, the H+ ions in proton conductors or holes in p-type semiconductors and some (very rare) conductors.

I think this is the main one where it breaks down for me