Here is a hint. Search out industrial electrically operated 1" ball valves and look at the massive size of the motor they use and then see if you still think you can adapt a hobby servo to do the task. Not saying it's impossible as there are very high torque servos available but it will not be simple. The proper non-flexing bracket assembly you will have to come up with will be a challenge in itself.
As someone already posted, see if you can get by with a solenoid operated (on/off) valve, it may to cheaper and easier in the long run, especially if you don't have a need to regulate the flow rate.
Lefty