I would suspect you have a weak kidney. The knees can become weak due to this kidney issue. Being in sports and exerting yourself, especially hockey where you are in cold weather, you are not as sensitive to dehydration feelings as you would if you were in hot weather. Proper hydration also consists of getting good electrolytes into your body as well as water.
The average person needs water at the following rate:
Take your total body weight and divide by 2. That number is the amount of water in ounces that you need to drink each and everyday. Along with that, you should consume 1/4 teaspoon of "air dried sea salt" in conjunction with each quart of water you drink. This puts the electrolytes in your body that will give you proper hydration. The typical white table salt you buy in stores like the Morton Salt, for instance, is terrible for you and has loads of chemicals added. Avoid that junk. If you drink ANY diuretic drinks like, sodas, coffee, tea, alcohol, commercially prepared fruit drinks, energy drinks, etc., these all dehydrate you and you will need to add more water to the total to compensate for the water loss due to these diuretic drinks. Take the total ounces of the diuretic drinks and multiply by 1.5 and add that total to the original total to come up with the proper amount of water you need to drink each day.
Because you are exerting yourself, you will need to add more water and salt to your regimen when you are exerting yourself. Be aware that your body loses water at the following rates: 60% kidneys, 24% persperation, 12% lungs, and 4% G.I. tract.
good luck to you
CNT, B.A. biology & chemistry
Advanced nutritional research