That's what I thought, but the more I research it the more I'm realizing I can't find anything negative (apart from hydrolocking, which with a fine mist is near impossible to do at fast idle). I'm going to give this a try right before I change my plugs. From reading about how it's done it can take anything between 2l or 3l up to 20l of water to finally get clear water coming out of the exhaust. If you think about it, lots of turbo cars have water injection installed, and a few cars from 30+ years ago also had small water bottles under the bonnet that were slowly added to the cylinder to clean it to keep it in tip top condition. Plenty of stories of mechanics doing this to rough running engines prone to carbon build up and running like a dream afterwards.
