Welcome to the gastroenterology community! Throughout the day, an average person should drink 2 liters of water and if you are taking laxatives I would recommend you drink at least 2 1/2 liters of water.
Oh, and it seems like it works best if I take it separate from meals, and don't drink much water during meals (because water dilutes the acid that is important for digestion, I think). And don't drink it immediately after the water turns clear for best effect. Wait 30-60 minutes whenever possible and see if it makes a difference like it seems to for me.
More water is better, but I take more than one packet to get enough relief. This is on top of a strong oral medication (Amitiza) and magnesium. With Miralax, I get the stuff in the bottle and take 1 1/2 capfuls once a day and as needed.