I was planning on building a water-powered rocket. I also wanted to know how high my rocket might go. Could someone help me figure out, how to calculate thrust produced by a rocket engine?
If you know the mass flow rate q and the exhaust velocity v, the thrust f is the product of q and v.
If the engine is running in a test stand, measurement of the thrust might be easier than to measure both mass flow rate and exhaust velocity.
For the measurement of thrust look at this question.