So would a 9 foot drop onto cement, but people still do that. I think dropping into water would be easier if you stay on the unicycle. It’s all about surface tension, and I think the tire would have a moment to take the impact and break up surface tension, making it easier for you to go through.
Yeah, it would definitely get the water moving out of the way, but if you go in crooked it might hurt more! Hence the risk. Stay on and hope to control your landing angle, or jump free and have more mobility? At that height I’d probably just be chicken to jump in the first place… 