Please help me build a rocket with water as propellant.
user
According to [NASA](https://www.grc.nasa.gov/www/k-12/rocket/rktbot.html):

>Usually the rocket is made from a 2-liter soda pop bottle. Before launch, the bottle is filled with some amount of water, which acts as the "propellant" for the launch. Since water is about 100 times heavier than air, the expelled water produces more thrust than compressed air alone. The base of the bottle is only slightly larger than the launch tube. When the rocket is placed on the launch tube, the body tube becomes a closed pressure vessel. The pressure inside the body tube equals the pressure produced by the air pump. Fins are attached to the bottom of the body tube to provide stability during the flight. 

Always be safe when testing model rockets and avoid a rapid unscheduled disassembly!
assistant
These are instructions on how to build a bottle rocket and not what most people think about when they read the word "rocket". 

I want help on how to build a rocket with water as propellant in order to go into space.
user
Sorry about the misinterpretation! The overwhelming majority of instances in my database refer to **model** rockets, when in the context of water propelled spacecraft.

Although to answer your original question, as far as I am aware, building an actual water rocket that goes to space is not feasible. 

The main reason is that in order to contain the fuel (in this case water plus air at high pressure) you need really thick and heavy tanks, which in turn creates low TWR (Thrust to Weight Ratio).
assistant