Hydration is unique in health: it is universally relevant, broadly understood at the level of "drink water," and almost entirely covered in myths once you scratch the surface. The reason is partly cultural — everyone has an opinion — and partly economic: bottled-water companies, sports-drink brands, and wellness influencers all benefit from making hydration feel complicated.
Below are eight of the most stubbornly repeated claims, each examined against the evidence. None of these is intended as medical advice; if you have a clinical reason to monitor your fluid intake, talk to a doctor, not a hydration tracker.
1. "You need eight glasses of water a day"
The original source is a 1945 US Food and Nutrition Board recommendation of ~2.5 L per day — including the water in food. Drop the food clause, round to "eight 8-oz glasses," and the meme writes itself. The actual adequate-intake values from EFSA (~2.0 L women / 2.5 L men) and the US Institute of Medicine (2.7 L / 3.7 L) include all fluids and food moisture combined, and are explicitly population averages.
For a fuller treatment, see How much water do you really need? Your number depends on body mass, climate, activity, diet, and life stage. Eight is a memorable round number, not a target.
2. "Coffee dehydrates you"
This claim survives almost entirely on plausibility. Caffeine is a mild diuretic, therefore caffeinated drinks must be net-dehydrating — right? At moderate doses (the equivalent of three to four cups of coffee a day for habitual drinkers), no. Killer et al.'s 2014 controlled crossover trial in PLoS ONE found that coffee and water produced no meaningful difference in 24-hour hydration markers.
Heavy doses in caffeine-naïve people can produce a transient diuretic effect, but for the vast majority of regular drinkers, coffee is water with a tax. The same goes for tea and most sodas. Alcohol is the actual diuretic to worry about.
3. "If your urine isn't clear, you're dehydrated"
Clear urine is not the goal. Clear urine usually means you are drinking more water than your body needs, which is at best wasteful and at worst the early end of hyponatraemia (low blood sodium). The clinical target is pale straw — the colour of a light beer or a chamomile tea. Anything from clear to light yellow is fine; anything from medium yellow to amber suggests topping up.
Also: vitamin B supplements turn urine bright neon yellow regardless of hydration. Beetroot makes it pink. Don't panic.
4. "Drinking water with meals dilutes your digestion"
This one cycles around social media every few years as if it were ancient wisdom. It isn't. There is no credible mechanism by which sipping water with a meal meaningfully alters gastric acid concentration; stomach acid is produced continuously in response to food and is not a fixed reservoir to be diluted. A 2014 review in the World Journal of Gastroenterology found no support for the claim.
Drinking litres of cold water in one sitting may slow gastric emptying slightly. Drinking a normal glass with a meal does nothing detrimental. Some cuisines — Indian, Japanese — traditionally have tea with meals for a reason.
5. "Thirst means you're already too late"
The grain of truth: by the time thirst registers, you are typically about 1–2% below optimal body water. The leap people make: therefore, you must drink constantly, ahead of thirst, to "stay ahead." For sedentary adults in temperate climates, this is unnecessary at best and counterproductive at worst.
Thirst is a perfectly serviceable signal at normal activity levels. Where it becomes unreliable is in two specific cases: older adults (the thirst response dulls with age) and prolonged high-intensity exercise (where sweat losses outpace thirst). For everyone else, thirst is fine. The reason an app helps is not that you can't feel thirsty — it's that you can be too busy to notice that you are.
The body has had a long time to evolve a fluid-balance system. Most "you need to override it" advice is selling you something.
6. "You need a sports drink during normal exercise"
Sports drinks are formulated for prolonged endurance efforts — broadly, more than ninety minutes of continuous exertion at moderate-to-high intensity, in heat, where electrolyte loss through sweat becomes significant. For a 30-minute jog or a standard gym session, water is what you need; the calories and sodium in a sports drink are a net negative for general health.
ACSM (American College of Sports Medicine) guidelines and a long line of trials agree: below ~60–90 minutes, water plus a balanced subsequent meal beats any commercial isotonic drink. Above that threshold, electrolyte replacement starts to matter — and even then, a banana with water often outperforms a sugared sports drink.
7. "Alkaline water is better for you"
This is the cleanest myth in the list, because it is the most testable. The stomach maintains a strongly acidic environment (~pH 1.5–3.5). Any water you drink, regardless of its incoming pH, is instantly equilibrated. Bicarbonate from the pancreas then alkalises chyme as it leaves the stomach. The systemic bloodstream is held tightly at pH 7.35–7.45 by a buffer system that does not care whether your kettle's water was pH 7 or pH 9.
Drinking alkaline water does not measurably affect blood pH (which is good, because if anything did, you'd be in trouble). The category exists because someone realised you can sell water for eight times the price if you put a number on the bottle.
8. "More water always means better skin"
Severe dehydration absolutely affects skin turgor and appearance. Going from mildly-thirsty to adequately-hydrated is unlikely to produce a visible difference beyond a few hours of fluid redistribution. A 2015 University of Missouri study looking at skin hydration after adding 2 L of water per day to a normal baseline found very small effects on stratum corneum hydration, and none on skin elasticity or appearance.
Skin condition is largely determined by genetics, age, sun exposure, sleep, and skincare. Drinking water won't hurt; drinking more water than you need almost certainly won't help.
What is true, in two paragraphs
Most adults do well to land somewhere in the 2.0–3.5 L of total fluid per day range, including food moisture. Thirst is a usable signal for most people in most conditions. Pale-straw urine is the visual cue. Coffee, tea, and most other drinks count. Sports drinks are for endurance events. Alkaline water is a marketing category. Skin is mostly other things. Older adults, athletes, pregnant or breastfeeding people, and anyone with a clinical condition should treat their own number as a deliberate decision, not a meme.
And if you'd like a small piece of software that helps you hit that number without thinking about it — built quietly, on-device, with no sense that any of this is complicated — that's what Drimin is for.