I was just going to add that in RARE cases (such as what Rosebud mentioned), people who drink more water than their kidneys can handle may suffer water intoxication, where sodium in the body becomes diluted, causing behavoiral changes or even brain damager. Probably wouldn't cause one's brain to explode though!

One caution, though. I saw a recent segment on CNN (Fox?) on people who swig from the same water bottle all day long, just refilling it. They went to a gym and took samples from everyone's water bottles. Only the bottles that were newly opened tested clean. ALL the other ones had highly elevated levels of bacteria in them, and some even tested positive for e. coli!

So drink your water. Just wash the container from time to time.