How Much Water Should You Drink a Day?

A coffee with breakfast, a few sips at lunch, then a big guilty glass before bed because someone said you need eight. Most people have no idea whether that adds up, and the honest answer is simpler than the rule.

Here is what health bodies actually advise, what counts toward it, and the signs that you need more.

Before and after: the same ordinary day

Same amount. Spread out, with food doing part of the work.

Rewind: what the health bodies say

Behind the counter, I heard this question more than almost any other. Totals from drinks and food:

• The US panel says about 20% of that water comes from food. That leaves roughly 9 cups of drinks for women and 12 to 13 for men.
• The panel gives no glasses-a-day rule, and a 2002 review in the American Journal of Physiology found no studies showing that everyone needs eight glasses, so healthy people can mostly let thirst guide them.
• You need more with heat, exercise, fever, vomiting, diarrhea, pregnancy or breastfeeding.

Rewind: what counts

• Water, milk, tea and coffee. The NHS counts all of them. The US panel found caffeinated drinks hydrate about as well as caffeine-free ones.
• Juice, in small amounts. The NHS suggests one small glass a day, because of the sugar.
• Food. Fruit and vegetables carry a lot of water.

Hidden tip: your salad is a drink

UCLA Health puts cucumber and iceberg lettuce at about 96% water, romaine at 95%. Watermelon is around 92%.

Hidden tip: thirst fades with age

MedlinePlus notes that some people lose their sense of thirst as they get older. I'm sixty-seven; I believe it. Don't wait to feel thirsty. Tie a glass to breakfast, your pills, the afternoon paper.

Signs you need more

• Strong thirst or a dry mouth
• Peeing less, or dark urine
• Dry skin, tiredness, dizziness

The easiest gauge: pale yellow, like light straw.

Yes, you can overdo it

Colorless urine can mean too much. Cleveland Clinic says more than about a liter an hour is probably too much, and the risk is higher for people with kidney, liver or heart conditions. If a doctor has limited your fluids, follow that. Ask your pharmacist, too. We like being asked.

Cheat sheet: daily water

If your day looks like the before, don't chug at night. Start with one glass at breakfast.