No, they are not the same, and the difference matters in the places these waters are used. Distillation boils water and condenses the steam, leaving dissolved solids and organisms behind in the boiler. Deionization passes water over exchange resin that swaps out charged ions. Both make very pure water by one measure, and they fail in completely different ways.
Two different definitions of pure
Deionization is judged by conductivity, because its entire job is removing charged particles. Freshly deionized water can read extremely pure on a meter while still carrying uncharged organic molecules and living bacteria, neither of which a resin bed is designed to catch. Distillation is judged by what could not travel with the steam, so it deals with salts, metals and organisms alike, but light volatile compounds can carry across unless the distiller finishes with a carbon post-filter.
How each one fails
Deionizing resin exhausts. When it does, it stops holding what it was holding and can release accumulated ions back into the water, sometimes in a slug, which is why laboratory systems monitor output continuously. Resin beds also grow biofilm if they sit warm and unused. A distiller fails more visibly: it scales up, it slows down, and the boiling chamber needs descaling. Neither is a set-and-forget device, and both cost real money per gallon compared with any household filter.
What either has to do with your house
Very little, usually. The one honest overlap is ion exchange, which is what a water softener does selectively: hardness, in the USGS definition, is dissolved calcium and magnesium, and a softener trades those two for sodium rather than stripping every ion in the water. If you came to this comparison because of scale or a mineral taste, you want that selective version on the main line. Our water softener installation page covers what fitting one actually involves.
Questions people ask about is distilled and deionized water the same
Which is purer, distilled or deionized water?
It depends on the measure. Deionized can show lower conductivity, while distilled deals better with bacteria and organics. Laboratories often use both in sequence.
Can I substitute deionized water where distilled is specified?
For an iron or a battery it usually behaves the same, since both lack dissolved mineral. Where sterility matters, deionized water is not an equivalent.
Is softened water the same as deionized water?
No. A softener exchanges only hardness ions for sodium, so softened water still carries plenty of dissolved solids and is nothing like deionized water.