if you have hte ability to test it, i would though, just out of curiosity.. i know the creek water around here is extreamly alkaline
i used creek water that was sometimes running and sometimes stagnant and i think it was like a natural compost heap and actually added many nutrient's definitely not in tap water. But the idea of testing it is obviously a no harm idea, because god knows it could be a waste runoff or overflow creek. eww.
it coud be good or bad i think. a buddy of mine used tap water for months and then he used creek water and it messed the ph up. and it caused the plant to go into shock. but i dont know for sure. just be carefull, and watch for any changes
on the topic of water would it be ligit to bring a couple bottles of water when you go to visit your grow site? like just regular bottled water?