I remember reading a few years ago about a follow-up study on the
e-coli disaster in Walkerton, Ontario by Health Canada.
The study did pretty extensive urine testing to determine if there was a risk of long-term kidney damage that didn't show up on initial assessments. They also tested for everything imaginable under the sun, in case there are other long-term health risks to e-coli which we currently don't know of.
A number of subjects tested positive for an enzyme which is only known to occur in the urine of people with degenerative heart disease. A small percentage did have heart disease, but the rest had only one thing in common: they all drank more than six litres (a little under two US gallons) of water a day. Most did it for supposed health reasons, and were highly resistant to change. It is possible that drinking that much water simply causes the same enzyme with no damage, but there's no way to know.
Having said that, most people don't drink enough water. My father-in-law has coached a lot of Ontario & Canadian champion athletes & several non-medalling Olympians in various sports, and he always has problems getting his athletes to drink enough water off the track. This usually makes them over-hydrate in distance events such as marathons & triathlons, which effects your performance. There is a formula distance athletes use that uses distance ran, body weight, temperature & a few other factors to calculate how much you need to drink before & during a race. You have to adjust it to your particular metabolism by trial & error & there is a lot of guesswork involved with regards to the particular course, but is well-established among endurance athletes that over-hydration can be as bad as dehydration. I'll have to ask him more about this when he comes to visit in October.
(He recommends 4 parts unsweetened cranberry juice to one part water, by the way. Apparently sports drinks have more sugar and salt than your body can process under exertion.)
If you don't mind a little more rambling, I know that there is a bias against drinking while training in CMA (in China, at least). There is a belief that it interrupts the continuity of training. I usually follow this rule, but I break it during outdoor training in July & August.
In the two summers I trained in China, I drank crazy large amounts of water. (I boiled it & let it cool in glass jars. Bottled water cost too much.) Mind you, at one point I was drinking well over 10 litres a day, and I didn't feel quite right. Then I realized I hadn't peed in almost a week. The temperature hit mid-40's & 100% humidity every day for 10 weeks. I managed not to take water breaks during my 2 1/2 hour afternoon training sessions, though, since no one else did. I have no idea if that was a good thing or not.
