They mention this in the article, but bears repeating - if you don't want to get a kidney stone (and believe me, you don't) 8 glasses a day is probably not a bad idea.
No, You Do Not Have to Drink 8 Glasses of Water a Day. You Also Don't Have to Get Kidney Stones.
To put some perspective on that, I recently had one and it was the worst pain in my life. I asked some women who have had both a stone and a natural childbirth which was worse, and they said the pain is about the same.
The difference is that at least you know +/- about a month when you're going to have a child and can prepare; with the stone, you're just suddenly in excruciating pain.
Every nurse I talked to seemed to take sadistic pleasure in describing how painful it would be when it came out.
Still nothing could have prepared me for that amount of pain. It was truly horrifying.
This is why when given the opportunity to tell people to drink more water, I do it. I wouldn't wish that experience on anyone.