How much water you need
A practical daily fluid target is roughly 35 milliliters per kilogram of body weight, plus more for exercise and heat — for most adults that lands somewhere between 2 and 3.5 liters a day. The old “eight glasses” rule isn’t wrong so much as one-size-fits-all; your body size and activity change the number quite a bit.
This calculator starts from your body weight, adds fluid for the exercise you do, and — if you tick the box — accounts for being on a GLP-1. The result is total daily fluid from all sources, not just plain water.
Everything counts (not just water)
You don’t have to hit the target with plain water alone. All beverages count toward it — including coffee and tea, whose mild diuretic effect is far too small to cancel out the fluid they provide. Water-rich foods matter too: fruit, vegetables, soup, yogurt, and similar foods can supply a meaningful share of your daily total. If you eat a lot of produce, you need a little less from drinks.
The simplest way to hit the number is to make it steady and visible: a glass with each meal, a bottle you refill on a schedule, and a drink whenever you feel the first hint of thirst, headache, or fatigue. Dark yellow urine is your body’s cue that you’re behind.
Why hydration matters more on a GLP-1
GLP-1 medications like Ozempic, Wegovy, Zepbound, and Mounjaro do two things that quietly set you up for dehydration:
- They slow gastric emptying, so food and fluid move through you more slowly and you feel full faster — meaning you drink less without noticing.
- They cut your appetite sharply, and thirst often rides along with hunger cues, so the prompt to drink fades too.
That combination is behind two of the most common complaints on these drugs. Nausea is often worse when you’re even slightly dehydrated, and steady sipping helps settle it. Constipation — one of the most reported GLP-1 side effects — is driven partly by slower gut transit and too little fluid and fiber; water is half the fix (adequate fiber is the other half). Staying ahead on fluids won’t eliminate side effects, but it’s one of the cheapest, lowest-risk things you can do to reduce them. That’s why the GLP-1 setting here nudges your target upward.
A note on overdoing it
More isn’t infinitely better. Drinking very large volumes of water in a short window can dilute your blood sodium — a condition called hyponatremia that, while uncommon, can be serious. The goal is consistent hydration across the day, not chugging liters to hit a number. If you have heart failure, kidney disease, or take medication that affects fluid balance, get your fluid target from your doctor rather than a general calculator — this tool is educational, not medical advice.