Many people report feeling better when they drink lots of water during hep C treatment. However, there is no research about this, nor is there an official recommendation.
You may have to try trial and error to find out the best amount of water that is right for you. To get you started, you can try a personalized method based on the color of your urine.
If your output is pale yellow or clear, you are probably getting enough water. If your urine is dark yellow that means it is concentrated, and you need to drink more.