The difference between purified and distilled water is the difference between a standard and a technique. Purified describes an outcome, water whose dissolved contaminants have been reduced below a threshold, achieved by any method. Distilled describes one specific process, boiling water to steam and condensing it back. All distilled water is purified; most purified water is not distilled.
How each one is actually made
Distillation boils water in a chamber, lets the steam rise and leaves everything that will not evaporate behind in the boiling vessel: minerals, metals, salts and most microorganisms. The steam is condensed into a separate container as the finished product. Purified water is more often made by reverse osmosis, deionization, carbon filtration or a combination, pushing water through a membrane or exchanging ions on resin beds. The end results overlap heavily in what has been removed, but distillation is unusually thorough about heavy dissolved solids while some volatile organic compounds can carry over with the steam unless a carbon stage follows.
Taste and minerals
Both taste flat compared with good tap water, because the calcium, magnesium and bicarbonate that give water its character have been removed. The US Geological Survey describes hardness as dissolved calcium and magnesium, and it is precisely those minerals that distillation and reverse osmosis take out. That is why remineralization cartridges exist on many under-sink systems: they add a little of the mineral back for taste and stability. If you find bottled distilled water unpleasant to drink, that is not a fault, it is the definition of the product doing its job.
Which one for which use
For appliances that must see no minerals, distilled is the conventional choice: steam irons, CPAP humidifiers, humidifier reservoirs, car cooling systems and lead-acid batteries all specify it because any dissolved mineral will be left behind as scale as the water evaporates. For everyday drinking and cooking, purified water from a household reverse osmosis unit is cheaper per gallon, produced on demand at the tap, and involves no bottles. For laboratory or specific medical uses, follow whatever the equipment maker specifies rather than substituting one for the other on price.
Buying it versus making it
Buying either by the bottle is convenient for occasional use and expensive as a household habit, and it carries the plastic and the lifting with it. A countertop distiller makes distilled water at home, slowly and using a fair amount of electricity, which suits someone who needs a gallon a week for an appliance. An under-sink reverse osmosis unit makes purified water continuously at a dedicated faucet, which suits a household that just wants better drinking water. And if the reason you buy distilled is scale in the kettle or the iron, our water softener installation page addresses the cause at the main line instead.
Questions people ask about purified vs distilled water
Is distilled water purer than purified water?
Usually in terms of dissolved solids, yes. But purified is a standard rather than a method, and a good reverse osmosis system produces water that meets it comfortably.
Can I use purified water in my CPAP or steam iron?
Manufacturers generally specify distilled, because any leftover mineral is deposited as scale when the water evaporates. Follow the equipment maker's instruction rather than substituting.
Why do both taste flat?
Both remove the dissolved calcium, magnesium and bicarbonate that give water its flavor. Remineralization cartridges add a small amount back for taste on many home systems.
Which is cheaper for daily drinking water?
Purified water from an under-sink reverse osmosis unit, made on demand at your own faucet, is far cheaper per gallon than buying distilled water in bottles.