weight loss diets recommend to drink 8 glasses of water a day, also to brighten skin. during a day, I think I drink too much water. I doubt that is it really true or it's just my illusion. the problem is when i try to drink water in a glass then i feel awful while drinking. so how can i measure how much water i drink a day?
What you are concerned about is Hyponatremia. Essentially the conditions for that to occur are probably not something you are doing. For example:
Unfortunately, the symptoms of hyponatremia are similar to severe dehydration. The safest way to address both of those problems after you have been doing a high intensity workout is to use a sports drink that replenishes your electrolytes (see the article). Essentially, adding more water in this state will dilute your already low supply of electrolytes. The sports drink will help in either case.
Assuming you haven't just been doing a high intensity workout, and you are simply sipping water throughout the day, you are probably going to be just fine. Keep in mind that 8 glasses a day is a minimum recommended daily allowance. I personally drink roughly a gallon a day. According to the article linked to above I could go up to 1.6 gallons and still be OK. I don't know how I'd fit that in, but I could.
My office has a water filter, so I re-use a water bottle and fill it with the filtered water throughout the work day. Some people just can't drink cold water, and they need it room temperature. Filling the water bottle lets you have the water convenient to you and sip on it throughout the day. I'll have 1.5L in the morning, and another 1.5L in the afternoon (after lunch). I have another refillable water bottle that is .5L and I sip on that throughout my workout. I tend to work through two of those between the weightlifting and cardio work. By that time, I am set for my daily requirements.
Also keep in mind that when people recommend 8 glasses a day, they are talking about an 8oz glass (or .25L). That's only 2L a day.
There are a couple of ways, and surely my listings are not exhaustive, ultimately you have to decide what's most convenient for you.
My recommendation is to get a transparent water bottle so you can see how much water/liquid is in it whenever you fill it up.
Every time you fill it up you know exactly how much water you will be drinking and is very portable.
There are problems with this because you have to store the water somewhere and it may not be convenient to carry large containers of water! Also if you drink less/more than your large container, you have to do a little extra measuring and math to get your total intake.
This is very similar to my recommendation except you need a second utensil solely dedicated to measuring.
What works for me is to alternate between water and my favorite beverage. I drink one 12-16 oz glass of water, then a glass of whatever, then another glass of water, and so on. This is the only thing that has worked for me.
Here's a couple things that I try to do regularly to help myself get enough water:
I have found that one of the keys to hydration is to drink water throughout the day, not trying to drink the entire days allotment within a couple hours. If I try to drink too much water to fast then I wont feel well. If I spread it out throughout the day, then it seems to work best.
If you only drink 1 glass with each meal (3/day) and 1 at each snack time (2/day) then you're already at 5 glasses a day. One during excercise and one just after waking up, then you've got 7. Much easier when it's spread out during the day.
I have also found that keeping my salt/sodium intake to a moderate to low level per day helps keep me hydrated more easily. Sodium does cause you to retain water, but it also can work to dyhydrate you in the process. That would be why you shouldn't drink salt water.