I noticed the same today and only finished a bottle on a two hour ride. Because it's a lot cooler vs hot and humid summers, your body needs to sweat less to cool you down. I know I perspired for sure but significantly less than I usually do. It was about 8 degrees C this morning with a nice slap-me-in-the-face kind of wind. Good idea to keep drinking but you'll notice as your body sweats less, you'll need less water.