Firstly this is my first post on Physics Forums so hello to everyone. The question I have came about after experimenting with (soda pop) bottle rockets with my niece and nephew, and a certain video on youtube showing a Japanese guy strapped to a bunch of bottles (I estimate about 21, but it is hard to tell). There is quite a lot of suspicion on whether this is real or a doctored fake (although if it is fake, what exactly are they trying to guerilla-market here?). My brother and I have decided to try this but instead of using many soda bottles and the problem this has with theoretical instability due to the combined rocket 'exhaust' being so far away from the persons centre of gravity, we have come up with the plan to use two 19liter 'water cooler style' bottles which would put the twin exhausts only about 8 inches or so away from the spine (behind a alloy backplate for safety). I am doing some experiments with the failure pressure for these bottles before we get started, but the engineering is a bit tricky due to the neck design and I keep blowing out my plugs. I thought I would post here to get everyone's comments and advice before I invest any more time. With about 20psi and using the bottle alone, I can easily fire the thing over 30 feet high. SO, after that very long intro, here is my question: Will two 19Liter bottles have enough stored energy to lift a 75kg person a few meters off the ground (into a lake)? If so, how much pressure would I need? How high could I conceivably get? All the bottle rocketeers out there suggest the optimum amount of water is 1/3 the interior volume of your pressure vessel so I would have 12.6L between two bottles. The neck of the bottle is 44mm or 1 3/4" inside diameter. Some of the above rocketeers use additives to change the viscosity and increase thrust, but I would like to stay away from that due to the fact I will be near (and in) water. I have life insurance.