Drinking distilled water does not do anything dramatic. It hydrates exactly as any other water does, it is absorbed the same way, and the body regulates its own electrolyte balance from a far larger set of inputs than a glass of water. The differences that are real are modest, and they are about taste and about a small nutritional contribution.
What happens on the way in
The first thing distilled water meets is stomach contents, which are strongly acidic and full of dissolved salts, so within moments of swallowing it is chemically indistinguishable from any other water in the same stomach. Absorption in the intestine proceeds identically. The kidneys manage electrolyte balance against the body's whole intake, dominated by food, and adjust output accordingly. There is no mechanism by which the absence of a few milligrams of calcium in a glass produces a physiological event.
What you notice
Taste, immediately. Water's flavor comes almost entirely from what is dissolved in it, so distilled water reads as flat or insipid rather than unpleasant. Tea and coffee made with it are noticeably duller, because extraction depends partly on mineral content. Some people find they drink less of it simply because it is less appealing, which is worth knowing for anyone who struggles to drink enough. A remineralizing stage fixes all of that and is what commercial systems fit as standard.
What you forgo
A small dietary contribution. Drinking water provides some calcium and magnesium, more from hard supplies than soft ones, and distilled water provides none. The USGS classes water as soft at 0 to 60 mg/L as calcium carbonate through to very hard above 180 mg/L, so the amount forgone depends entirely on what your supply was. Against a normal diet the difference is small. It matters more where diet is already poor or intake is very high through heat or heavy work.
The one genuine caution
It is about volume rather than distillation. Drinking a very large amount of any water quickly can dilute blood sodium dangerously, and that risk is the same for distilled, filtered or mineral water: the water is the factor, not the purity. Endurance athletes and anyone drinking heavily in heat should be replacing electrolytes regardless of which water they use. Our drinking water guide covers remineralizing, which addresses both the taste and the mineral question at once.
Questions people ask about what happens if you drink distilled water
Does distilled water harm you?
No. It hydrates identically and is chemically indistinguishable from other water within moments of reaching the stomach.
What do people actually notice?
The taste. Flavor comes from dissolved minerals, so distilled water reads as flat, and tea and coffee made with it are duller.
Am I missing minerals by drinking it?
A small dietary contribution, larger if your supply was hard. Food provides the overwhelming majority of calcium and magnesium.
Is there any real risk?
Only the one common to all water: drinking a very large volume quickly can dilute blood sodium. Purity is not the factor there.