Actual hydration is a complex undertaking.
Water is absorbed in 2 main places in the body, the stomach and the large intestine. The body need the foods we eat to be in a very liquidy state to move it through the digestive system. So when we eat, the stomach will digest some of the food (carbs and proteins) and also hydrate the food to a very liquidy state. It will the pass this liquid slurry through the intestine (digesting lipids and absorbing nutrients) and then it travels into the large intestine where the body will absorb the excess water to resolidify the digested food before it is evacuated out of the body. How much water the stomach move into the body or out of the body depends on several factors. In short if the food does not have enough fluids with it during intake, the stomach will absorb water from the body to hydrate the food. If there is excess water in the stomach it will absorb it into the body. So fluid intake with foods normally stay with the food all during the digestion process. Fluids drank between meals will normally be absorbed into the body much faster. There are too many other factors that also affect hydration do discuss here.
Although some water is absorbed by the body in the stomach, electrolytes (Na, K, Mg and Ca) take up to 2 hours to be absorbed. Therefore electrolyte solutions (Gatorade etc...) should be taken about 2 hours before actual activity to get the best benefit. Also taking electrolyte solutions after activity will help replenish lost electrolytes. The average person gets plenty of Na from all the table salt (NaCl) in our diets however, most people are low in the other electrolytes, K, Ca, and Mg. Cramps can be cause by low levels of electrolytes, but they can also be cause by an imbalance of the electrolytes. Example: high levels of Na and low levels of K, which is the case of most people due to large consumption of table salt.
Also the body will hydrate better by drinking water in smaller amounts over a longer period of time instead of drinking a lot of water at one time. When large amounts of water are taken in at one time, the body will absorb it from the stomach. This large influx of water into the bloodsteam will raise the water level of the bloodstream. Elevated water level in the bloodstream will cause the kidneys to remove what it perceives as too much water. Therefore the water would be removed (sent to the bladder to be urinated out) and water actual never circulates through the body to hydrate the cells. This can cause a person to misinterpret the urinating as a sign that they are hydrated when in fact they are still dehydrated. Frequent urination and the urine being a light straw color are signs that a person is hydrated, but not always.
With all this said, I have coached a kid in the past that had a medical condition that caused him the dehydrate quickly a cramp up all over his body. We monitored him during practices and made him drink water and break often. For games, his doctor prescribed him an IV solution that the school nurse administered during half time of ever game. This was the only way he could finish a game.
Not knowing the athlete above, nor any medical condition he may have, my recommendations would be similar to what others posted. Drink a glass of water each hour or so, again not too much at one time. Drink a good electrolyte solution about 2 hours before practice/games and after practice/games to replenish what was lost. As far as supplements, taking Mg, K and Ca could help. When taking salt tablets just realize that when the salts tables hit the stomach, the stomach will dissolve it by absorbing water from the bloodstream (this is why some people get an upset stomach after taking them or other vitamins/mineral tablets). So, always drink plenty of water when taking salt tablets or they can contribute to dehydration in the short term by absorbing water from the bloodstream.. If you do take them, do it least 2 hour or more before practice/games, again drinking plenty of water. I personally would suggest more electrolyte solutions during the day as opposed to salt tablets. Just watch the sugar intake with electrolyte solutions, some are loaded with sugar.
Sorry if this was too long but I hope this helps.
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