Asking why shouldn't you drink distilled water usually means someone has heard a warning and wants to know whether it is real. There are four objections in circulation: the mineral one, the taste one, the fluoride one and the practical one. Three of them are weaker than they sound for a healthy adult on a normal diet, and the fourth is the one worth taking seriously.
The objection about minerals
USGS defines hardness as dissolved calcium and magnesium, and distillation removes both entirely, so distilled water contributes none of either. The objection treats drinking water as a meaningful mineral source. For most people it is a minor one next to food. Anyone on a restricted diet, or managing a condition where electrolyte balance matters, should raise it with a clinician rather than settle it from a web page.
The objection about taste
This one is true and it is the reason most households abandon distilled water rather than any health worry. Taste in drinking water comes largely from dissolved minerals and dissolved gases, and distillation strips both, which is why the result reads as flat or empty. Aerating it by pouring between containers helps a little. Adding mineral drops helps more. Coffee brewed with it tends to taste thin.
The objection about fluoride
Distillation removes fluoride along with everything else dissolved, so a household that switches its whole drinking supply loses whatever fluoride the public supply provided. Whether that matters is a dental question for your family, not a water treatment question, and it applies equally to reverse osmosis. It is worth knowing about rather than being surprised by it at a check-up.
The objection that actually matters
The practical one. Distilling covers small volumes slowly, so households that adopt it for everything end up storing water in open-mouth jugs, handling them constantly, and refilling from a machine that needs descaling. That is where contamination and neglect enter. If distilled water is meant to be your entire drinking supply, a plumbed system is usually the more reliable path, as our reverse osmosis buying guide sets out.
Questions people ask about why shouldn't you drink distilled water
Does distilled water leach minerals out of your body?
That claim goes far beyond the evidence. For a healthy adult eating an ordinary diet, drinking distilled water is not considered harmful by mainstream guidance.
Is distilled water safe for babies and formula?
Parents commonly use it for formula, but follow the formula maker's instructions and your pediatrician's advice, because fluoride intake is part of that decision.
Is it safe for pets?
Pets drink it without issue in ordinary circumstances, though most vets see no reason to use it in place of clean tap or filtered water for an animal.