You've read about drinking at least 8 glasses of water a day, and how critical it is to stay hydrated. I'm sure that might make you wonder - is it possible to drink too MUCH water?
The answer is YES, it is definitely possible, but for most people it is extremely unlikely. So it would be like never going outside at all because you might get hit by a meteor. Still, it is good to know the symptoms.
Water intoxication is known by many names. Some call it water poisoning, others call it hyper-hydration. In essence (to simplify greatly) what happens is that your blood gets too watery, and your body tries to keep this sort of thing in balance. So in order to get your blood back to normal, your body starts to allow the water to draw into the neighboring cells.
While you might not care too much if your fingers or toes get swollen cells, as you might imagine, your brain is a little more sensitive about these sorts of things. So if your brain starts to swell, you can have very serious issues including mental confusion, collapse, and even, in extreme conditions, death.
It's key to point out again that this doesn't tend to happen to people who are lounging on the beach drinking water. This is the sort of thing that happens to marathon runners who are running all day long and drinking water rather than sports drinks. Their body is sweating out salts, but the person is only drinking in water without salts. Their body gets out of balance - it becomes "too watery" - and they have problems.
Another way water intoxication happens is when they have game show types of contests where people chug water in gigantic amounts and try to see how much they can get into their system. Their blood gets more and more watery, their body gets wildly out of balance, and dangerous things happen as a result.
There was an example in 2008 where a woman took in 4 liters of water in less than 2 hours as part of a diet plan. She ended up dying. Other examples tend to include frat hazing activities and small children who are forced to drink massive amounts of water as a "punishment".
So, as with everything, moderation is the key. Never force people to drink water in large quantities. Adult human kidneys can process about a liter an hour but of course that's different for every person. If you're sweating, make sure you take in something with electrolytes. Sports drinks are good for that. Always talk with a doctor if you have any questions!