i go by the taste. it is easy for me to tell which is which even just drinking one with no comparison. the negative magnetized water is smoother and the positive is more lively, almost bitter or acrid in sensation.
i had some luck with hydroponics. the crop called for a more acid solution that kept wanting to go alkaline. i put positive magnets under the entire system and right up against the flow of water. my meter never budged from a perfect reading with no chemical adjustments. if i needed alkaline, i would have used negative pole.