Correct.
You don't feel thirsty until you're 2% dehydrated, and at 2% dehydration, your exercise capability has dropped by 10%.
Drink stuff thats tasty too, not plain water. Plain water makes you piss more, thus dehydrating you further, and doesn't make you wanna drink it.
Aim for approx 100ml/10 mins. However its person-specific.
You also wanna try and get about 40-60g* of simple carbohydrates (ie. sugar) into you per hour, plus minerals (Na+, electrolytes). Jaffa cakes are actually pretty good, and easy to eat/store.
*Thats for professional football - probably lower for trials.
That's during exercise anyway...
Prior to riding, you wanna keep your glycogen store high - google that :mellow: