Deionized water is made by pushing water through exchange resins that swap out charged particles, while distilled water is boiled and the steam condensed back into liquid. The difference matters because ions are only one class of impurity: deionization is blind to anything without a charge, and distillation is blind to anything that boils at a similar temperature to water.
How deionization works
DI resin beads carry exchange sites that trade hydrogen and hydroxide for the dissolved charged particles in the water. Those particles include the calcium and magnesium the USGS defines as hardness, along with sodium, chloride, sulfate and nitrate. The beads exhaust as they load, and once exhausted they stop working and can even release what they held. That is why DI is normally sold as a cartridge with a monitor or a fixed change interval rather than a set-and-forget appliance.
How distillation works
A distiller boils water in a chamber, carries the steam to a condenser and collects the liquid in a separate container, leaving the dissolved solids behind as scale in the boiling chamber. Anything that will not evaporate at that temperature stays in the pot, which covers minerals, most metals and salts. The trade is speed and energy: a countertop unit produces a batch over a few hours and needs the chamber descaled by hand on a regular schedule.
Where the two results differ in practice
Distillation deals with microbes and non-volatile contaminants in one step, while DI leaves organisms and uncharged organic compounds untouched unless a carbon stage sits alongside it. On the other hand a fresh DI cartridge can drive ion content lower than a single distillation run, which is why laboratories and car detailers use it. For a household the useful summary is that distilled is the safer default and DI is a specialist tool.
Neither one is a treatment plan for your house
Both processes make small volumes of very pure water for a specific job, such as filling a steam iron or topping up a battery. Neither addresses the water in your shower, your washing machine or your water heater, and neither tells you what your supply contains in the first place. If you have a hardness or contaminant problem, start with our water testing guide, then choose whole-house or point-of-use treatment on the result.
Questions people ask about di water vs distilled
Is DI water purer than distilled?
For dissolved ions, usually yes while the resin is fresh. For bacteria and organic compounds, distillation is the more reliable of the two.
Can I make DI water at home?
Yes, with a cartridge unit, but the resin exhausts steadily and needs replacing, so most households find a distiller or a reverse osmosis unit simpler.
Do either of them remove hardness?
Both do for the water they produce, since hardness is dissolved calcium and magnesium, but they only treat the small batch that passes through them.