Just to let you know: in this site, it is not forbidden for a user to have several accounts, but it is strictly forbidden to use them for up-voting yourself, or even worse, to down-vote an answer by more than one point.

@coquelicot I suggest we let moderators worry about such things, and you worry about the quality of what you write.

@Kranulis. Speaking about quality, the title of your question is "Why is the resistance of water so high?" (which is a physics question involving quantum mechanics), and inside the text, the question is "why water is such a danger for short circuits if the resistance is so high?", which is unrelated to the titular question, and is furthermore rather half baked: /continued

You first decided in the question that the resistance is high, which is relative and incorrectly stated at the least (as explained at the beginning of my answer). Then you say "water is a danger for short circuit" which may be interpreted in several ways, the most obvious one being: "Why is water considered to be able to create short circuits, a danger for electronic devices." Not exactly what I call a quality question.

@coquelicot I agree with your assessment of the question title & contents as stated. But this is a serious safety issue, and an awful lot of people get the issues confused, so while it could be (should be) more clearly & consistently stated, I think it is still worth answering as (I think) the question was really intended - i.e., "why is water + electricity so dangerous".

I must admit - a rather strange discussion......

In addition to manassehkatz’s answer, water is much more corrosive supplied with electrical current than without it. It can destroy conductors (potentially leading to more mechanical and electrical failures and ruining for the entire device). Exposure of water to direct current also generates H₂ (hydrogen gas), which is flammable, although it isn’t usually an actual fire hazard.