Two ways:
You don't have to log every glass as it happens. Counting bottles at the end of a ride and logging one total works fine. Forgot yesterday? Tell Claude "log 2 liters for yesterday" and it lands on the right day.
I ride in Texas. In July and August, a two-hour ride here can go through more water than a whole winter day, and the days I felt flat for no reason usually turned out to be the days I came home with a full bottle still on the bike. Writing the number down is how I caught that. If you ride somewhere hot, or you're stacking long days, a simple log tells you whether you're actually drinking or just carrying water around. It's also useful on rest days. The day after a long hot ride, you're still refilling the tank, and it helps to see whether you actually did.
Your hydration entries show on your weekly dashboard next to your rides, so you can see your intake alongside the days you rode. Claude can answer "how's my water intake?" if you want the trend, or compare it across weeks.
Honest answer: hydration is a log, not a metric. It doesn't feed your fitness or effort numbers, and RideTool doesn't score it, set targets, or nag you about it. It's a place to write the number down so you can see it next to your riding. Some riders log it all summer and ignore it all winter. That's a fine way to use it.