"Coffee dehydrates you." How many times have you heard this? There is a grain of truth behind this widespread belief, but the full picture is far more nuanced than a simple yes or no. Each beverage you drink contributes differently to your body's water balance, and understanding this is the key to accurate hydration tracking.
For decades, the prevailing wisdom was that caffeine is a diuretic and therefore coffee and tea cause net water loss. This is technically half-true: caffeine does temporarily reduce the kidneys' ability to retain water. However, this diuretic effect does not completely negate the hydration provided by the water in the beverage itself.
Research has conclusively demonstrated that moderate coffee consumption (3 to 4 cups per day) does not cause net dehydration in habitual drinkers.[1] In other words, coffee does not hydrate as effectively as plain water, but it still provides a meaningful net hydration contribution. So how do we quantify this difference?
The dehydration factor (DF) is a coefficient that represents how much of a beverage actually remains in your body as usable hydration. For pure water, this value is 1.0 — every milliliter you drink counts fully toward hydration. For beverages containing caffeine or alcohol, the factor is lower because these substances cause the body to excrete more water than it would otherwise.
The formula is straightforward: Net Hydration = Volume Consumed x Dehydration Factor
| Beverage | Dehydration Factor | Net Hydration per 200 ml |
|---|---|---|
| Water | 1.00 | 200 ml |
| Milk / Buttermilk | 0.90 | 180 ml |
| Fruit Juice (natural) | 0.85 | 170 ml |
| Sports Drink | 0.80 | 160 ml |
| Tea (black / green) | 0.70 | 140 ml |
| Coffee (filter / Americano) | 0.60 | 120 ml |
| Soda / Soft Drink | 0.50 | 100 ml |
| Alcoholic Beverage | -0.40 | -80 ml (causes water loss) |
A 200 ml filter coffee has a dehydration factor of 0.60. This means:
200 ml x 0.60 = 120 ml net hydration
So your morning cup of coffee contributes approximately 120 ml toward your daily water goal. This is a real contribution, but drinking the same volume of plain water would be nearly twice as effective for hydration.
Tea typically has a higher dehydration factor (0.70) than coffee (0.60) because it contains significantly less caffeine per cup. A typical cup of black tea contains 40 to 70 mg of caffeine, while a cup of brewed coffee contains 80 to 120 mg. Less caffeine means less diuretic effect, which means more of the water stays in your body.
Green tea is an even better option from a hydration perspective, with caffeine levels of 20 to 45 mg per cup. Herbal teas that contain no caffeine, such as chamomile or peppermint, have a dehydration factor close to 1.0 and are effectively equivalent to water for hydration purposes.[2]
Alcohol suppresses the production of ADH (antidiuretic hormone), the hormone that signals the kidneys to retain water. When ADH is blocked, the kidneys produce significantly more urine. The result is that you lose more water than the alcoholic beverage contained. This is why the dehydration factor for alcohol is negative: it does not merely fail to hydrate, it actively depletes your existing water reserves.
This explains why a night of drinking often results in a headache, dry mouth, and fatigue the next morning. These are all symptoms of dehydration caused by alcohol's interference with the body's water conservation mechanisms.
Most water tracking apps count every beverage equally: 200 ml of coffee equals 200 ml of water. This is scientifically inaccurate and can lead to a false sense of adequate hydration. Suu is different.
Suu includes over 100 beverage categories, each with a scientifically assigned dehydration factor. When you log a coffee, tea, juice, or any other drink, Suu automatically calculates the net hydration value and applies it to your daily goal. No more guessing whether your third cup of coffee "counts."
Simply select what you drank, and Suu does the math. Your daily hydration dashboard reflects your true hydration status, not just the total volume of liquid consumed.
Suu automatically calculates net hydration for coffee, tea, and 100+ other beverages using the dehydration factor system. Accurate tracking, smart reminders, personalized goals — all free.