Distilled water is not harmful to drink. It is water that has been boiled to steam and condensed back, leaving behind essentially everything that was dissolved in it, and the result is about as pure as domestic water gets. The objections to it are real but modest, and they are about taste and about where you get your minerals rather than about safety.
What distillation actually leaves behind
Because the water changes phase, anything that does not evaporate with it is left in the boiling vessel: dissolved minerals, salts, heavy metals, nitrate, fluoride and most contaminants of concern. That is why distillation is used where the water source is genuinely doubtful. It also removes calcium and magnesium completely, so the output is as soft as water can be, well below the USGS soft classification of 0 to 60 mg/L as calcium carbonate. Volatile compounds that boil near water are the exception and can carry over unless the unit is designed for them.
The mineral argument, in proportion
Drinking water contributes some dietary calcium and magnesium, and distilled water contributes none. For anyone eating a normal diet that difference is small, since food supplies the overwhelming majority of both. The concern has more weight where diet is already poor, where intake is very high in hot climates or heavy work, or where someone drinks nothing but distilled water for long periods. It is not a reason to avoid it, and it is easily answered by remineralizing, which is what commercial systems do deliberately.
Why it tastes the way it does
Flat. The taste of water is largely its dissolved minerals, and removing all of them removes the character with them. Most people describe distilled water as insipid rather than unpleasant, and coffee and tea made with it are noticeably duller, which is why remineralizing cartridges are sold for exactly this. It also absorbs carbon dioxide from the air on standing, which makes it slightly acidic and adds a faint sharpness. Our drinking water filter guide covers the remineralizing options.
When it is the right choice
Distillation is worth its cost and slowness where the source is unknown or badly contaminated, where nitrate or arsenic are present and a membrane is not practical, or for specific uses such as steam irons, humidifiers, aquariums and CPAP machines where any mineral content causes scaling. For everyday household drinking water, reverse osmosis achieves a comparable result far faster and with much less energy, which is why it has largely replaced domestic distillation.
Questions people ask about is drinking distilled water bad for you
Is distilled water safe to drink?
Yes. It is not harmful. The objections concern taste and mineral content rather than safety, and both are easily addressed.
Will it leach minerals from my body?
No. Drinking water contributes a small share of dietary calcium and magnesium, and food supplies the overwhelming majority of both.
Why does it taste flat?
Taste in water comes largely from dissolved minerals, and distillation removes all of them. A remineralizing cartridge restores the character.
When should I choose distillation over reverse osmosis?
Where the source is unknown or badly contaminated, or for irons, humidifiers, aquariums and CPAP machines. Otherwise reverse osmosis is faster and cheaper to run.