People need to drink enough water every day.Sometimes，you might not finish drinking your glass of water before （1）

going

going

（go） to bed.You might want to drink it the next morning. （2）

But

But

have you ever wondered if it is still safe to drink？
    "If you have clean water in （3）

a

a

clean glass，you're fine to drink it for a day or two，"Kellogg Schwab from the Johns Hopkins University Water Institute in the US told Times.
    But you may find that it（4）

tastes

tastes

（taste） strange.That's because after about 12 hours the carbon dioxide（二氧化碳） in the air reacts with the water in your glass，slightly lowering the PH level of water.
    Also，there might be more microorganisms（微生物） in your water if you leave it out overnight.Microorganisms grow much （5）

more quickly

more quickly

（quick） at room temperature.These microorganisms can stick to your glass.They can make you get sick more easily.But if you clean your glasses very often，this （6）

will not/won't be

will not/won't be

（not be）a problem.
    In countries like the US and UK，people often drink water directly from the tap.This is OK——however，tap water can't be stored for a long time.Most experts say that tap water has a shelf life（保存期限） of six months，according to Zane Satterfield from West Virginia University，US.After six months，there is less chlorine（氯） in the water and bacteria（細(xì)菌） start to grow.You'd better （7）

not drink

not drink

（not drink） the water，or you may get sick.
    What about plastic water bottles？Schwab said people should be （8）

careful

careful

（care） with them.If you leave a bottle of water in the sun or a car （9）

for

for

a long period of time，the plastic produces a chemical（10）

called

called

（call） BPA.This chemical can cause heart disease and cancer.