Is this for real? I thought water and electricity shouldn’t mix!
At low voltages you can get away with it. Water actually isn't a very good conductor but the impurities in it can be. This is why saltwater is a much better conductor than fresh water.
For high current use, like a Club 500, we used to run the brushed motor in under water and with 2.4v for around 20 minutes. Not sure how much good it did but it was a routine that we all followed and it certainly made nice black water.
It looks like Martin has used washing up liquid, or something similar. We didn't do that!