I'm trying to figure out why I'm sometimes quite thirsty in the middle of the night after a big ride.

Let's say I go on a 60 mile ride and don't drink as much water as I should have.

If I get home and drink, say, a quart or more of water, does that take care of the deficit, or can my body not absorb the water fast enough? Do I have to space out my rehydration?

I have had this happen to me once or twice. Not after the rides I have posted about in another thread but the evening after less strenuous rides. Have also felt the need for water the next morning as well.

I never wake because I'm thirsty, rather the need to lose fluid! However, I've got into the habit of drinking a large glass of water before bed and another first thing in the morning after my first cup of coffee.

After a ride, especially now in the high heat and humidity down here, I make sure I drink a lot during a ride, then drink a 20oz pint (yes, we have bigger pints in the UK and I still use them here!!) of water or water/electrolyte after a ride.

I use an Isotonic supplement on rides and after a ride I still cannot get enough liquid inside me. I normally get normal by 8 pm when the last cup of tea is drunk. Nights are not a problem but I get up around 4 am and the first thing is coffee.

I've had trouble in the past after long hot rides getting water back in. Even after drinking far more than should be necessary I would still wake up significantly under my normal weight. Then I started upping my salt intake after a ride and it seemed easier to rehydrate.

Given that excess sodium causes one to retain water, it seems reasonable that lower sodium levels, which occur after a long hot ride, would result in less water being retained.

Hydration the day BEFORE you ride is very very Important..

You also need electrolytes, etc. See other threads on ride hydration.

Beer works here

gregf83 has fingered one of the factors.

You may need to use urination as a guide. Frequency during and after the ride? Colour? Volume? Do you feel bloated or generally upset in the stomach after drinking after a ride?

Only a certain amount of fluid can be absorbed per hour through the gut, and the same applies off the bike. Maintaining a good electrolyte balance in the stomach itself assists.

I have been using some BCAA (Branch Chain Amino Acids) in my water during and post ride. It seems to keep hydration and recovery balanced. I live in the desert SW where a couple rides have been in the 100+ heat already. It seems that I need to intentionally push the water more than ever. I have also broken an old rule of mine and had a small glass of Pepsi post ride. Sure tastes and feels good.

I try to use urination as a guide. Remember, you're not just rehydrating, you're flushing waste products out of the muscles.

My real question was: "Can I rehydrate by drinking a lot of water at once after a ride?" and the answer seems to be "no."

Keep drinking until your urine is clear. Personally I like to hydrate over a period of hours at a moderate pace. When I've woke up thirsty in the night like you were describing I always figured I was still dehydrated.

Drink when you're thirsty, but not a quart/liter all at once.
I very much enjoy a glass of water/juice/beer/whatever when I am very thirsty. Not so much drinking a large volume of fluid.

That is consistent with my experience. A ride 2 weeks ago I didn't drink enough, only (4) 750ml bottles on a 4 hour ride with temperatures in the 80's and 90's. It took 7 hours after the ride before I began to feel back to normal, and couldn't drink enough, waking up several times through the night to drink more. Sure don't like that feeling.

Sips. Many, but low volume. Otherwise, by drinking a whole lot at once, you are upsetting the electrolyte balance in the stomach that then inhibits the absorption, that then maybe makes you feel bloated. And it stops you from drinking more later on when it really does count.

Bingo. It's a plumbing issue. You're dehydrated throughout the body, but when you dump some fluid into your gut, much of your freshly rehydrated blood will head on to the kidneys and lose significant water before that water can be used to bring you back to full hydration. It's going to take a while to rehydrate, but you can minimize the time by:
1. Don't get as dry (duh). Drink more when you ride and before, even if you need to then take a natural break now and again.
2. Drink many smaller doses over several hours rather than one big hit.
3. Keep moving. part of re-equilibrating blood and other tissues is mixing the fluids. Contraction of muscles helps do this, so go for a walk in the evening after you ride.

Pale, straw-colored urine indicates good hydration, but doesn't tell you if you have replenished depleted electrolytes, so electrolyte drinks should be used, not only water.
Over-hydration can be dangerous if it causes blood electrolytes to become too dilute. That's hyponatremia and can kill.

Artmo is 100% correct but I like to use the urine as a general guide because in the past I quit hydrating too soon and that delayed my recovery quite a bit. This was a good thread with the hot weather of summer on us. I rode 50 today and by the time we finished it was 91 deg and 17 mph winds. I am toast. Feeling like the 60 years old that I am.

Correct. I often have a second wave of thirst. It's no big deal to me though.....doesn't mean I should have taken on more in the first wave. I don't think you can or should really guzzle your way to instant rehydration. No scientific studies to back that up however.

When I am very dehydrated, it takes days to feel normal again. On hot rides with substantial climbing I usually come home 5 or 6 pounds light, but I have finished 11 pounds light. That's around a gallon and a half! Since the body can only absorb around a quart per hour, at best, it's going to take an effort to put back 1.5 gallons.

I think the color of your pee is a good way to check to a certain extent, but if you're really dry and you pound down a bunch of water, your pee will be clear and you will still be dehydrated.

I agree about the electrolytes and minerals and I feel best if I keep eating during the ride, (regular food), and I love a big bowl of soy ramen at a Japanese restaurant after. It's salty and has liquid and carbs, yum.

What is the objection to drinking more while riding. Start with a good glass of water before pedaling and keep it up.

No objection. I think I generally drink enough during a ride, and usually pee once or twice on a 60 mile ride. But I am sometimes thirsty at night, and I'm trying to figure out why.

In my case I can sweat a lot more than I can absorb on a hot climbing ride.

On longer rides with intensity or in heat, you go into fluid deficit. It has to do with the ability of the stomach to absorb a lesser amount than what you are. sweating out, the function of which is to keep your core temperature stable. Don't forget also that at higher intensity, you are breathing out larger quantities of moisture than, say, at tootling pace.

The ability of the stomach to enable absorption of fluid is dependent on electrolyte balance. That balance also has an influence on the uptake of some nutrients from the stomach.