As others have suggested, you need to know your own needs.
I'm late to the party, but a few suggestions:
1) Learn to monitor your hydration level. There are a lot of good online resources with urine color guides. Look at several of them – you'll see that the color rendering differs considerably, but the average is about right.
2) Monitor your hydration level and record your water consumption on a series of hikes under various conditions. You'll need this information in order to project your needs. Unless you're trail-running, you'll need less than you did when you were racing, but under hot conditions, you can still lose a lot of water to sweat, and dry conditions will up your losses through breathing and evaporation.
3) Monitor your hydration regularly during all hikes that are long enough or dry enough that water matters. If water is plentiful, you don't need to pay much attention to things. If conditions are dry, you want to stay reasonably well-hydrated. Staying reasonably well-hydrated gives you a margin of safety and means you need to *carry* less water.
4) Use your information from suggestion #2 to project your future needs, and reliable information about potable sources on your route to plan out how you'll meet them. It won't hurt you to go into a little bit of deficit (just as you did when you were racing), but you need to be sure you won't hit clinically relevant dehydration levels even if you're delayed or if a potential source doesn't pan out.
There's very little you can do to alter your needs, but if you do these things, you'll be able to minimize unnecessary water carrying while still staying safe and healthy.
A few additional thoughts:
5) It's not a bad idea to record your thirst perceptions while you're following suggestion #2. If you find that thirst is an adequate indicator of your hydration level, it makes life a little easier. It doesn't work for everyone, especially as people get older. I know at least two people who will just forget to drink if they don't think about it. One of them occasionally approaches clinically relevant levels of dehydration (after noticing he hasn't peed all day).
6) Unless you're trail-running, I'd be surprised if your hydration needs pushed you up against the limits of what your system could readily absorb, even if you're drinking plain water. "Sports drinks" are unnecessary.
7) If you're sweating out a lot of electrolytes, you're going to need to replace them. If you're eating real food, you'll already have plenty of potassium. (Do the calculations on your daily potassium intake. You'll probably be surprised how much potassium real food has.) If you're eating real food that doesn't have salt added, you *won't* have enough sodium. (Do the calculations on how much sodium is in a pound of gorp.) There's a reason why animals in most parts of the world are always looking for salt. If you have a lowish sodium diet at home and don't add some extra salt when you go into the mountains for long days, it's not that hard to reach clinically relevant levels of hyponatremia.
Cheers,
Bill S.
