放了一夜的水到底还能不能喝？

Do you drink water that’s been left sitting out overnight, or even for another day? Have you noticed it tastes different?

你有喝过隔夜水，甚至是放了一天的水吗?如果喝过，你有感觉到味道不一样了吗?

Tap water that has been left to sit out slowly begins to acquire an off taste. Many assume that this is because of microorganisms. Treated water's added chlorine will take care of small communities of these little guys, but at room temperature they begin to multiply rapidly and can really get the party started. Even with clean water and a clean glass; one sip introduces a host of germs to the mix, in addition to whatever the water may have picked up by ambient dust.

只要把自来水放在那里不动，就会慢慢开始产生异味。对此，许多人都认为这是微生物在搞鬼。虽然自来水中所添加的氯气可以消灭这些小家伙，但在室温下，它们开始迅速繁殖，重新聚集并于水中狂欢。即使用干净的玻璃杯装上干净的水，但除了环境中遍布的灰尘以外，你一口下去也会掺入一系列细菌。

But that’s not what makes old water taste stale. For that we can thank carbon dioxide. After about 12 hours tap water starts to go flat as carbon dioxide in the air starts to mix with the water in the glass, lowering its pH and giving it an off taste. But it’s most-likely safe to drink.

不过，这并不是令水味道变坏的原因，罪魁祸首其实是二氧化碳。大约12小时后，空气中的二氧化碳开始与玻璃杯中的水混合，降低其pH值并使其具有异味。而这时候的水，一般还是可以安全饮用。

However, back to those microorganisms. If you use a dirty glass day after day, there is more of a chance of unruly bacteria making themselves known; a risk that increases if you share the glass with another mouth as well. But assuming you use a fresh glass every few days, you likely won’t have a problem. Unless. Unless the rim of the glass has been touched by dirty fingers; and especially if those dirty fingers went unwashed after using the bathroom. With those kinds of germs left to multiply in a left-out glass of water, who needs enemies?

说完罪魁祸首，再继续说说那些微生物。如果你日复一日地使用脏掉的玻璃杯，那么细菌必然欢聚一堂。当你与别人共用玻璃杯时，风险也会增加。但只要你每隔几天就把玻璃杯洗得干干净净，基本上不会有任何问题。那么，瓶装水呢?

As for plastic water bottles that have been left out in the sun or the car, step away from the bottle, warns Dr. Kellogg Schwab, director of the Johns Hopkins University Water Institute, if it's a reusable water bottle that may contain BPA. “A chemical called bisphenol-A, or BPA, along with other things used to manufacture plastic can leach into your water if the bottle heats up or sits in the sun,” he explains. BPA, as you likely know, is a hormone disruptor that has been tentatively linked to everything from heart disease to cancer. Schwab also adds that plastic used for commercial bottled water isn’t meant to be washed or refilled, so use only one time and recycle. Or way better, don’t buy them at all; use a refillable water bottle instead.

约翰斯·霍普金斯大学水资源研究所所长Kellogg Schwab博士警告说，如果一瓶水暴露在阳光下，或是留在过汽车中，那就远离那瓶水。他对此解释道：「如果塑料瓶加热或暴露在阳光下，一种名为双酚A或称BPA的化学物质以及其他用于制造塑料瓶的物质都会浸入水中」。

你或许也知道，BPA是一种激素破坏剂，与心脏病和癌症都有所关联。Schwab博士还补充说，瓶装水的塑料瓶不要清洗后重新装水，用过一次就送去回收利用吧。当然，不买瓶装水更好，用可重复使用的水瓶装水为佳。

If you’re concerned about drinking water that has been stored for a long time, it can also become unsafe to drink. Zane Satterfield, an engineer scientist with the National Environmental Services Center at West Virginia University, says most experts agree that tap water has a shelf life of six months. “After that point, the chlorine dissipates to the point that bacteria and algae start to grow.” And especially if you store water in a warm and/or sunny spot, or in a container that has not been properly cleaned and sealed.

此外，长时间存放的饮用水，也会变得不安全。西弗吉尼亚大学国家环境服务中心的科学家Zane Satterfield表示，大多数专家都认为自来水的保质期为六个月。「在那之后，氯气已经消散到了细菌与藻类可开始生长的程度」。

当然，要是你将自来水存放在温暖或阳光充足的地方，或是没有经过适当清洁与密封的容器中，那可就更糟糕了。