Of all the things Wave asks you to keep an eye on, water is the one people are most surprised to see. It seems too basic to matter. Then they start logging it and notice the afternoon headache has a cause.
What being a little dry does
You do not have to be anywhere near dangerously dehydrated for it to show. A loss of one or two percent of body water, which is a normal morning for someone who slept eight hours and had two coffees, is enough to raise heart rate, dull concentration, drop your mood, and make a workout feel harder than it should. Thirst lags behind all of that. By the time you feel it, you have been running short for a while.
It shows in the record, too. Resting heart rate reads a few beats high. Heart-rate variability reads low. The morning scan on a dry day looks a lot like the morning scan after a short night, which is one reason Wave asks about both before it tells you why today feels the way it does.
How much
The old rule of eight glasses is not wrong, but it is a rule of thumb for an average person on an average day. A better starting point is about 30 to 35 milliliters per kilogram of body weight, roughly half an ounce per pound. For a 175-pound person that is around 85 to 90 ounces, or 2.5 to 2.7 liters, across the whole day, from everything you drink and a good part of what you eat.
Then adjust. A hard workout, a hot day, a flight, alcohol and a lot of caffeine all push the need up. Fruit, vegetables, soup and yogurt all count toward it.
Wave sets a daily goal from your weight and nudges it up on days with a logged workout. It is a target to aim at, not a rule to obey.
The easiest way to know
Color. Pale yellow means you are fine. Darker than that, drink. Clear all day, you can ease off. It is not glamorous, and it beats any calculation.
The second easiest way is the pattern in the log. Most people are not short of water all day. They are short of it in the morning, when they go from waking to their first meeting on coffee alone, and again in the late afternoon. A glass on waking and a bottle on the desk fix most of it.
What to expect
Nothing dramatic, which is the nature of the thing. Fewer afternoon dips. A workout that feels the way it should. A resting heart rate that stops wandering on days you cannot otherwise explain. It is one of the cheapest improvements in the whole record, and one of the first the coach will point at when the week has been oddly flat.
Wave is for general wellness. Anyone with heart or kidney disease, or taking medication that affects fluid balance, should follow their doctor’s guidance on how much to drink.
