Both end up with very few dissolved minerals, but they get there differently and they leave different things behind. Deionization runs water through ion exchange resin that swaps out dissolved ions. Distillation boils water and condenses the vapour, leaving anything that will not evaporate in the chamber. That difference decides which one suits a given job.
What each process actually removes
Deionization is specific to ions: calcium, magnesium, sodium, chloride, sulfate and the rest. It has no effect on uncharged material, so bacteria, particles and many organic compounds pass straight through unless a separate filter handles them. Distillation removes anything non volatile, ions and organics and microorganisms alike, but volatile compounds that boil below water can carry over with the steam unless the still is designed to vent them.
Where the starting water matters
Deionization consumes resin in proportion to the ion load, so the harder your feed water the faster the cartridge is spent. That is why serious DI setups put softening or reverse osmosis upstream. Distillation does not care about the ion load in the same way, but hard feed water scales the boiling chamber and forces frequent descaling. Reading your utility's annual Consumer Confidence Report, which the EPA maintains a finder for, tells a city customer what they are starting from.
Which to use for which job
For rinsing cars, windows or solar panels with no spotting, DI is the right tool because it is fast, needs only water pressure, and can be plumbed to a hose. For appliances specifying distilled water, or for anything where sterility and organics matter, distillation is the safer bet. For drinking water at home, neither is the obvious answer: reverse osmosis at the sink delivers similar water continuously at far lower running cost.
Ownership and running cost
A DI cartridge is consumed and thrown away or sent for regeneration, and the cost scales directly with how many gallons of hard water you run through it. A distiller uses electricity for every gallon and demands manual descaling but has no consumable media. Neither is a whole house solution. If your underlying complaint is hardness across the house, our water softener installation guide is the sensible place to start instead.
Questions people ask about deionized water vs distilled
Is deionized water the same as distilled water?
No. Both are low in dissolved minerals, but deionization removes only ions while distillation also leaves organics and microorganisms behind.
Can you drink deionized water?
Deionization does not disinfect and resin beds can host bacteria, so DI systems sold for rinsing are not intended as a drinking water supply.
Which is better for a car rinse, DI or distilled?
DI, by a wide margin. It runs at hose flow on line pressure, while making enough distilled water to rinse a car would take many hours.