Posted: 10/01/2017 at 19:27
It's not the quantity of water, it's the timing.
Excess water has to pass through your kidneys then into the bladder.
If you are drinking all the way to the start of the race, there's a good chance you'll need the loo.
The solution is this:
Note the time the race starts and stop drinking two hours before that.
Any excess fluid will have passed through your system before the race starts.
Within ten minutes of the start of the race, you can drink another load. That won't have enough time to get through your kidneys into the bladder. After that it doesn't matter since the process shuts down under race effort. That is normal.