How water affects the resistance of a material at different voltages?

as I said before in recent science projects I have been studying the effect of water on the electrical resistance of materials that absorb water such as wood and sponge (the reason for the majority of my weird questions regarding water and electricity). I first tested wood but decided that wasn't a fair test due to the other chemicals in the wood, so here I am doing sponge as there are no chemicals in the material that affects how the water changes the resistance. As I said with the wood, I am calculating resistance by reading the current going through it at 9v, then dividing the voltage by current, and for the sponge, I got 87621 ohms. My question is would resistance stay the same as I go up the voltages to say 300 volts (I have no intention of testing it with that as I said lol) if not how much would it reduce by? I heard that the chemicals in the water may affect resistance as voltage goes up but would there be no space for that to happen in the water that is soaking an object due to the very low volume?

Specifically how much would the resistance change as I went up the voltage, as I have a common consensus that it will change, but by how much? This YouTuber in the video linked below did an experiment with high voltages, and whilst there is a reduction of resistance there isn't much... Is this roughly what I'd expect to happen in most circumstances with tap water and wet things soaked with tap water?