Why don`t you carry a big PET filled with water when you go out for work. Also it is difficult to say the exact cause of yellow urine, since many things can cause it. But you can make educated guess by eliminating one suspect at a time by trying to see if avoidance of the vitamin supplement for two days changes the urine color. Also note that NEVER NEVER take high doses of single vitamin in one shot. Excessively large doses of vitamins WILL HARM YOUR BODY than helping it. Even the vitamins needed should be taken in three or four doses spread over the day, even if it means SPLITTING YOUR VITAMIN PILL IN TO 4 PIECES. Forget vitamin pills, if you are eating well & balanced.
By the way there are also a number of diseases like STD, Kidney diseases or diabetes all can cause Yellow urine. But first think of the simple causes that could be. Also try-out the Triphala tea to help your kidney a little. Always remember nobody sitting far away can replace your good doctor next door.
Good luck, relax and take care.
Nature has answers for all, but our job is to find the diamonds among coal.
From Asprin to Viagra all comes from Nature.