About one glass of water, 150–200 ml (5–7 oz), for every alcoholic drink after the first one of the day. Alcohol makes you lose about 10 ml of water per gram of alcohol, so a first beer still adds a little water, but past about 20 g of alcohol every beer, glass of wine or shot takes water away. A shot of spirits takes some away even as your first drink.
Why you need water after alcohol
Knowing how much water to drink after alcohol starts with one number: alcohol makes your kidneys let go of more water than usual. The classic measurement, from a 1942 study, is about 10 ml of extra urine for every gram of alcohol. So “how much water after alcohol?” really means “how many grams of alcohol did I have?”. For the usual drinks:
- a 500 ml (17 oz) beer at 5% has about 20 g of alcohol;
- a 150 ml (5 oz) glass of wine at 12% has about 14 g;
- a 40 ml (1.4 oz) shot of spirits at 40% has about 13 g.
Beer is mostly water, so the first one still leaves you with some water to spare. A shot has almost as much alcohol as a glass of wine and very little water, so it takes away more than it brings. If you want the science behind these numbers, with the formula for each drink, I wrote it up in why alcohol dehydrates you, beer vs wine vs spirits. Here I’ll stick to the practical part: how much water to drink, and when.
The 20 g daily allowance
When I built Hydra, I ran into a problem. If a beer counts by the water in it minus the water its alcohol costs, a 500 ml beer adds about 300 ml. Log five beers and you would be 1.5 litres closer to your water goal. That is obviously wrong.
So Hydra gives alcohol a daily allowance of 20 g, about one 500 ml beer. Within it, each drink counts with its own factor: beer ×0.6, wine ×0, spirits ×−2.2. Past it, the water in the drink stops counting and only the cost of the alcohol is left: beer ×−0.4, wine ×−1, spirits ×−3.2. A first beer still counts as some water, but you can never reach your goal on beer, and every drink after the first asks for water.
One thing I want to be clear about: 20 g is not a safe or recommended amount of alcohol. It is only the point where Hydra stops counting the water in alcoholic drinks. How much alcohol is fine for you is a question for your doctor, not for a water tracker.
How much water for each drink
Here is what one drink does to your water in Hydra, and how much water brings you back. “Past 20 g” means the drink comes after you’ve already had about one large beer that day.
| Drink | First of the day | Past 20 g | Water to offset |
|---|---|---|---|
| Beer, 500 ml (5%) | +300 ml | −200 ml | 0 / 200 ml |
| Beer, 330 ml (5%) | +198 ml | −132 ml | 0 / 140 ml |
| Wine, 150 ml (12%) | 0 ml | −150 ml | 0 / 150 ml |
| Spirits, 40 ml (40%) | −88 ml | −128 ml | 90 / 130 ml |
A drink that lands across the 20 g line counts partly each way. A second glass of wine after a first one, for example, comes out at about −90 ml, between the two columns. You don’t need to do this maths at the bar. The pattern is what matters:
- First beer: no extra water needed.
- Every large beer after it: about 200 ml (7 oz), a full glass.
- Wine past the first glass: about 150 ml (5 oz) per glass.
- A shot: about 90 ml (3 oz) even as your first drink, about 130 ml (4.4 oz) after that.
Worked examples: a night out
Let’s put it together. Each example starts with no alcohol earlier that day, and the water is what Hydra would ask for, rounded up to the next 10 ml.
- Two 500 ml beers. The first adds +300 ml, the second about −200 ml. Your net total is still about 100 ml up, yet Hydra asks for 200 ml (7 oz) of water. I explain why below.
- Three 150 ml glasses of wine. 0 ml, about −90 ml, then −150 ml. That is about 240 ml (8 oz) of water: one big glass.
- A beer, then two shots. +300 ml, then about −130 ml for each shot. About 260 ml (9 oz) of water.
- Four 40 ml shots. About −90, −105, −130 and −130 ml. About 450 ml (15 oz): almost two glasses.
Look at the last one. Four shots are only 160 ml of liquid, but they ask for nearly half a litre of water. That is the strength of the drink at work, not the amount.
How Hydra’s “Offset the alcohol” hint works
When a drink takes water away, Today shows a hint under your net hydration: “Offset the alcohol with X ml of water”. Here is how I built it:
- Every drink that takes water away adds its cost to what you owe for the day.
- Water you log after it pays the cost back. So does any drink without alcohol, by its own factor: tea or coffee counts like water, an electrolyte drink counts 1.5 times.
- More alcohol never pays it back, not even a first beer that still adds water. You don’t offset alcohol with alcohol.
- The amount is rounded up to the next 10 ml, and the hint goes away once it’s paid.
That’s why two beers ask for 200 ml even though your net total is still positive: the water in the first beer doesn’t cancel the alcohol in the second. It is a deliberate choice. The 10 ml per gram figure is the cautious estimate, and newer studies found a smaller effect in some cases. I’d rather the hint be a little strict, and you drink a glass you didn’t strictly need, than have it tell you you’re fine when you aren’t.
Your daily goal doesn’t change after drinking. The alcohol lowers your net hydration, and the offset water is what brings it back. If you haven’t worked out your goal yet, the daily water intake calculator uses the same formula as the app.
Before, during and after: a simple plan
- Before: start the evening on track with your goal. In Hydra, water you drink before counts towards your day, but it doesn’t pay off alcohol you haven’t had yet.
- During: have a glass of water with every drink after the first. Plain or fizzy, it doesn’t matter: sparkling water hydrates like still water.
- Spirits: a small glass of water, about 130 ml, per shot.
- After: one more glass before bed covers whatever is left.
- Next morning: your usual drinks count again, and coffee counts like water, so your morning cup isn’t working against you.
Water isn’t the only option. Electrolyte drinks are kept by the body better than water, so in Hydra they count 1.5 times: about 135 ml of an electrolyte drink offsets what 200 ml of water would. I compare them properly in whether electrolytes hydrate better than water. Plain water works fine; it just takes a little more of it.
Water and hangovers
This article is about hydration only. Water replaces the fluid alcohol makes you lose. It doesn’t undo alcohol’s other effects, and I won’t claim it prevents or cures a hangover. Don’t force down litres of water at the end of the night either: drinking very large amounts in a short time isn’t better, and spreading it over the evening is easier on you.
These numbers are for healthy adults. If you have a heart or kidney condition, take medication, or have been told to limit fluids, follow your doctor’s advice rather than an app.
Know how much water your evening needs
Hydra counts every drink by what it’s worth and tells you how much water offsets the alcohol, right when you log it. Free on iPhone and Apple Watch.
