Some folks will drink the recommended amount of water in large portions, which then acts as a diuretic because it is more water than the body can handle at one time.
It is important that you not drink a lot of water just before a meal, and wait an hour or so after eating before drinking water. This is to avoid diluting your stomach's digestive juices.

The instructions that come with the colonix kit tell you to drink a glass of water after you drink the fibre drink. That can be too much at one time for some folks (like me!). I wait about 20 minutes after the fibre drink and then drink more water.
If you feel you are drinking enough water, then your symptoms should start to subside after the first week. Detox symptoms can be uncomfortable. You could also consider reducing your dosage initially if you think you are detoxing to quickly. I found that I could not switch to 4 Paranil capsules in the second week. I had to work up to that gradually, going from 2 capsules to 3 capsules and getting to 4 capsules about 5 days into the second week.