The target in each version
| Version | Daily target | In litres |
|---|---|---|
| 75 Hard | 1 US gallon | ≈ 3.8 L |
| 75 Soft | 3 litres | 3.0 L |
| 75 Medium | Half your bodyweight in ounces | ≈ 2.2 L at 150 lb |
Note that a US gallon is 3.79 litres, not the imperial gallon of 4.55 litres. If you are outside the United States and reading the rule as “a gallon”, you may be aiming at three quarters of a litre more than the program asks for.
What counts toward the total
This is the most argued-about detail in all three challenges, and the honest answer is that it depends which retelling you follow.
- Plain water — counts everywhere, no dispute.
- Unsweetened tea and coffee — counted by most versions, because they are still fluid. Strict readings of 75 Hard count only plain water.
- Sparkling and flavoured water — generally fine if unsweetened.
- Alcohol — never counts, in any version, and is banned outright on 75 Hard.
Pick one reading on day one. The rule is not really about the fluid — it is about whether you keep the definition you started with when it becomes inconvenient on day 50. Write down whether coffee counts, and then stop relitigating it.
When a fixed target is a bad idea
Most coverage treats the water rule as harmless. For most healthy adults it is — kidneys can clear well over a litre an hour, and the usual outcome of a gallon a day is inconvenience rather than harm. But the target is fixed, and your body is not:
- Kidney disease, heart failure, or liver disease — fluid targets can be genuinely dangerous. This needs a doctor's number, not a challenge's.
- Medication affecting fluid balance — diuretics, some antidepressants and drugs affecting antidiuretic hormone all change what is safe.
- Drinking far past thirst, fast — pushing litres in a short window to “catch up” before bed is the pattern that dilutes blood sodium. Spread it across the day instead.
Scaling to your own size, as 75 Medium does, is the more defensible rule of the three. A 50 kg person and a 100 kg person do not need the same volume, and no version of these challenges was written with your health history in front of it.
How people actually hit 3.8 litres
Willpower is not the constraint — remembering is. The reliable method is to anchor water to events that already happen rather than to the clock:
- One glass on waking, before anything else.
- One with each meal — that is three more without a decision.
- One before and one after each workout. On 75 Hard, that is four.
- One in the evening, well before bed, so the last litre is not at 11pm.
A single large bottle you refill a known number of times removes the arithmetic entirely: two 1.9 L refills is the gallon, three 1 L refills is 75 Soft's target. Front-load the day — nearly everyone who fails this rule fails it after 8pm, trying to drink a litre they should have had at lunch.
Electrolytes
At these volumes, especially with two daily workouts or heavy sweating, plain water alone is not the whole picture. You do not need an expensive powder — salting your food normally covers most of it. But if you are drinking a gallon a day, training outdoors in heat, and eating a very clean low-sodium diet at the same time, that combination is worth paying attention to rather than ignoring.