My advice is common knowledge among the backpacking crowd but I'll put it on the table for folk who perhaps have never heard this concise and helpful saying.............."Clear and Copius"

Yup......watch your urine stream and if your yellow it's time to increase your intake of fluids. Copius refers to intervals. You should be evacuating often and it should be fairly clear. My bailer (obviously mis-named) sees plenty of use early in the day as it is common for me to drink a litre or more of water before shoving off. Then it is a simple matter of keeping a close watch. Your stream tells the tale. Dark golden yellow and your pushin the limits. Expect a headache brought on by dehydration soon thereafter.