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Sometime in the last three years, the electrolyte aisle went from two products to forty. There are sticks for your water bottle, tablets that fizz, sachets marketed at people who do not exercise, and at least one brand whose entire personality is sodium.

I get asked about this constantly, usually in August, usually by someone who has been feeling foggy at four in the afternoon and suspects a deficiency. Here is the version I give in clinic, minus the diplomacy.

Sodium Is Basically the Whole Story

When you sweat, you lose water, and you lose minerals, but the losses are wildly uneven. Sodium dominates. Depending on the person and conditions, sweat carries between 200 and 2,000 milligrams of sodium per liter, and a heavy sweater in real heat can lose a liter or more in an hour.

Potassium losses run far lower, in the low hundreds of milligrams per liter. Magnesium and calcium appear in trace amounts that food covers without difficulty.

Which means most of the marketing has the emphasis the wrong way around. A product built around magnesium and potassium, with a modest sprinkle of sodium, is addressing the parts of the problem that were never urgent. If you are replacing anything after a hot commute, it is sodium.

When You Actually Need It

Three situations genuinely call for electrolyte replacement.

Sustained sweating beyond about ninety minutes. A long run in July, a hot yoga class, a full day outdoors in humidity. Below that threshold, water and your next meal handle it.

Illness involving vomiting or diarrhea. This is the original use case and the one with the strongest evidence behind it by an enormous margin.

Heavy sweating combined with a low sodium diet. If you are eating mostly whole foods and cooking without much salt, you have less to draw on than someone living off restaurant meals.

For a normal August day involving air conditioning, a walk to the train, and a desk, water is sufficient. The four o'clock fog is far more likely to be sleep debt, a lunch made entirely of carbohydrates, or the third coffee arriving on an empty stomach.

Why There Is Sugar In It

This is the part people try to optimize away, and it is worth understanding before you buy the zero sugar version.

Sodium and glucose share a transporter in the small intestine. Glucose arriving alongside sodium pulls both across the gut wall, and water follows. This mechanism is why oral rehydration solution saves lives in cholera treatment, and it is arguably the single most useful piece of nutrition science of the twentieth century.

A small amount of sugar in a rehydration product is doing real work. For a short recovery drink, the effect is modest. For genuine dehydration, it matters considerably.

What Underperforms

Coconut water is constantly recommended, but it is a poor sweat replacement. High potassium, low sodium, which is precisely the wrong ratio for what you lost.

Drinking large volumes of plain water during prolonged heavy sweating carries an actual risk. Diluting your remaining sodium can produce hyponatremia, which sends endurance athletes to hospital every summer. It is rare, and it lands people in emergency rooms every year, which puts it firmly outside the realm of the theoretical.

Anything promising cellular hydration, which is not a measurable thing and appears mainly on packaging.

If You Are Buying One

Look at the sodium per serving first. Under 200 milligrams is a flavored drink. Somewhere between 300 and 1,000 is functional.

Liquid I.V.'s original Hydration Multiplier sits at 560 milligrams of sodium per stick, with 11 grams of sugar from cane sugar and dextrose. Those numbers work for the situations above. The sugar is the component most people want removed, and it is the component performing the transport described earlier.

Worth saying plainly: I would ignore the packaging. The brand markets a proprietary hydration technology, but the actual mechanism is sodium-glucose cotransport, which has been public knowledge since the 1960s and appears in every rehydration product that works. The formula is sound. The story on the box is decoration.

Two limits. Eleven grams of sugar suits a genuinely draining day and is pointless at a desk, so this belongs in a cabinet, not in a daily routine. And the sugar-free version swaps glucose for allulose and amino acids, which gives away the one thing that made the original effective.

Homemade works too, for what it is worth. A quarter teaspoon of salt and a tablespoon of sugar in a liter of water with lemon juice is close enough for most purposes and costs almost nothing.

The Caveat That Matters

If you have high blood pressure, kidney disease, heart failure, or take medication affecting sodium or potassium, do not add a high-sodium product to your day on the strength of an article. Ask your doctor, who has your bloodwork.

For everyone else, the honest summary is that this category is overselling to a market that mostly does not need it, while remaining genuinely useful for the smaller group that does. Work out which one you are before you buy a month's supply, and be suspicious of any brand that implies you were dehydrated all along and simply hadn't noticed.