Originally Posted by
Carbonfiberboy
I never drink water without thirst. IOW, I drink to thirst. That prevents hyponatremia, which is at least as great a medical risk as dehydration. Only experience can tell one how much electrolyte one needs to create thirst. One doesn't always get thirsty when dehydrated. Thirst depends more on electrolyte balance than it does of dehydration level, which can be independent of that balance. One also will have a much better electrolyte balance on long rides if one always eats a low salt diet, which sounds backwards but is nevertheless how it works.
.
I agree with most of your post with a couple of exceptions. First, I think hyponatremia is extremely rare with cyclists. I've heard of it, once with a friend who was part way through RAAM and had to be hospitalized and another time with a guy who was doing a 150 mile climbing ride on a hot day and he wasn't eating. I think if a cyclist is eating or at least taking electrolytes the risk is minimal. I know people have died from it during marathons, but these are people who spend 6+ hours running with nothing but water.
The other thing is the "drink only when thirsty" idea. This may work for some but certainly not everyone every time. When I do a hot climbing ride I cannot keep up with the fluid loss and have to start forcing water early in the ride. I typically come home from a hot ride (6 hours, more or less) 5 or 6 pounds lighter. I tried to ration water once, still drank a bunch, and was 11 pounds lighter after the ride. To me, thirst doesn't enter it and I must make a conscious effort to drink.