In the northern hemisphere we are entering the hottest part of summer. It's easy to drink when riding but I struggle with remembering that good hydration begins the day before a ride. If you ride a lot that means it needs to happen every day.
So I'm writing this as much to drill it into my memory as any other reason.
Drink when you're off the bike. A lot. Even when you're not thirsty. By the time you are thirsty you are likely approaching a state of mild dehydration. It can be hard to remember, I definitely have to remind myself, but it can make the difference between a good ride and a terrible one.
As I'm a copious sweater I will supplement my off the bike drinks with electrolytes just to be sure i'm topped up before I head out. My favorite off the bike drink is a liter of water with 2 sis tablets and 8 packets of tru-orange. Just a couple calories from the tabs and it's pretty tasty so it goes down fast. I try to make it a summer habit to keep a bottle of water or tru-orange with me at all times.
I notice a huge difference on hot days- I can go harder and farther than I can if I don't pre-hydrate the previous 12-24hrs.
On super hot days (i'm very heat sensitive so that means +85F to me) when I haven't paid attention to drinking off the bike I've gotten into situations o the road where my stomach can't empty what I'm taking in fast enough and I've hydration-bonked with a stomach full of sloshing liquid.
Drink more and be safe out there.