Hydrogen fuel cell vehicles like the Toyota Mirai are the future, as some would have us believe, citing that the only emissions from these futuristic vehicles is a harmless fluid known as dihydrogen-monoxide. That’s good old fashioned water folks, and Toyota says it’s perfectly harmless to drink…but, uh, you shouldn’t. Huh?

In an interview with Automotive News, a Toyota executive admits that nobody at the automaker has actually tasted the water, though they are running extensive tests on it. Toyota says that these tests confirm fewer organic impurities than milk, and with a ph level of just 5 or 6 its actually less acidic than rain water or beer. So why doesn’t the automaker recommend people drink it?

Because the water is only as clean as its input. The hydrogen fuel stacks don’t sterilize the water, so if you’re driving through a smoggy area you could end up drinking the very pollution you’re trying to avoid putting into the atmosphere in the first place. Hyundai doesn’t seem to share Toyota’s concerns, having put together a demonstration drinking trial using the Tucson Fuel Cell vehicle to grow a vegetable garden.

Is Toyota just being overly cautious in light of a nationwide “unintended acceleration” epidemic that really wasn’t? Probably, and I can’t say that I blame them. On the other hand, it does make one wonder just how “clean” hydrogen cars really are. Consumers are probably going to ask this question time and again, and Toyota should probably come up with a more definite answer.

Would you take a swig of water that you knew came from a fuel cell tailpipe?