If you are asking this question because you are deciding what to buy, the interesting difference is not the water, it is the machine. An under sink reverse osmosis system and a countertop distiller both give you water with almost nothing dissolved in it, and they ask completely different things of your kitchen, your electricity and your attention.
How each machine produces water
A reverse osmosis system works continuously and quietly in the background, using household line pressure to push water through a membrane and fill a small storage tank, sending the rejected fraction to the drain. A distiller works in batches, boiling a chamber of water and condensing the steam into a collection jug over a period of hours. One is a plumbed appliance you forget about, the other is a countertop appliance you operate. That single difference drives everything else about living with them.
Output and waiting
Reverse osmosis delivers on demand from the tank through a dedicated faucet, so a glass is instant and a large pot takes a little patience while the tank recovers. A distiller gives you exactly what its chamber holds per cycle, and the next batch is hours away. For a household drinking and cooking daily, that batch limit is the constraint that eventually pushes people to plumbed systems. For a single person or an occasional need, a distiller is perfectly adequate.
What each one costs to run
A distiller boils every drop it produces, so electricity is its running cost and it is not trivial for daily use. A reverse osmosis system uses no electricity at all in most designs, running on line pressure, but it does send water to the drain while producing. So one trades power for water and the other trades water for power. Where you live and what you pay for each decides which annoys you more, and for most US households the reverse osmosis side comes out ahead on daily use.
Maintenance and what wears out
A reverse osmosis system needs prefilters changed on schedule, a postfilter for taste, and a membrane replaced after several years, plus an occasional tank pressure check. A distiller needs the boiling chamber descaled regularly, because everything removed from the water is now baked onto the inside of it, and the carbon pod in the lid replaced. Neither is difficult. The distiller job is dirtier and more frequent, and the reverse osmosis job is easy to forget until the taste tells you.
Installation, space and who they suit
Reverse osmosis needs a cabinet with room for the tank, a hole in the sink deck or counter for the faucet, and a drain connection, which makes it awkward for renters and impossible in some kitchens. A distiller needs a countertop, a socket and somewhere to store the collection jug, and moves house in a box. Renters, small kitchens and people who cannot drill choose distillers for that reason alone. Our reverse osmosis water filter cost page covers what each side of that decision runs.
Questions people ask about difference between reverse osmosis and distilled water
Which system is quieter?
Reverse osmosis, easily. It makes an occasional trickling sound as the tank fills, while a distiller runs a heating element and a cooling fan for the length of every batch.
Does a distiller waste water like reverse osmosis does?
No, a distiller uses only what it boils, apart from a small residue drained from the chamber. It spends electricity instead, which is the tradeoff between the two designs.
Can I have both?
Some households do, using reverse osmosis for daily drinking and cooking and a small distiller for appliances specified for distilled water. For most people that is more equipment than the problem needs.
Which one do renters usually choose?
A distiller or a countertop reverse osmosis unit, because neither requires drilling a faucet hole or connecting to the drain. Both come with you when the lease ends.