My friend's hydration comes from drinking coffee only, 4 to 5 cups daily. is this sufficient ?

No way.: The caffeine is coffee is actually a diuretic, so not only would coffee be a poor rehydration liquid by itself, it actually promotes urination and further loss of fluid. Bad choice.

Not sufficient: Coffee is dehydrating in nature in spite of its water content. 4-5 cups of coffee provides a bit more caffeine than the amount considered average intake of 1-2 cups a day. Encourage your friend to take a glass if water before every cup of coffee to ensure reasonable level of hydration.

No: Caffeine dehydrates and is not a good choice for hydration. Water or an electrolyte solution is better. Thanks for asking.

No: Depending on where you are located..........daily need of fluid is around a liter........all kinds of liquid together.

Hypocritically, no: Coffee is a diuretic; while the body can compensate somewhat, this isn't a good way to be hydrated and is a risk for kid*ouch*ney *ouch* stones *ouch*

No: Caffeine is a diuretic, it makes you want to void more. Not a good source of hydration and excess caffeine not good for your health. You need to try to drink 6-8 cups of water a day to hydrate yourself

Unlikely: Coffee contains caffeine which can act as a diuretic. This means much of the water in coffee actually is quickly excreted. Your friend should make an effort to drink at least 1.5 liters of water per day - maybe more.

Not really.: One must take in about 1.5 L of fluid per day to maintain adequate hydration and excrete waste. Some of this water comes from the food you eat. Your friend must have more intake that he lets on. 5 cups is not enough. Unless of course they are very large. Caffeine is a diuretic, but its effects are blunted by frequent use and dehydration.