The state of your RO over time is dependent upon the water you feed it. Is it receiving raw water? Well or city? Do you have a softener upstream? The answer to your question will vary based on your response to those questions. An RO membrane can last for 10 years or be damaged in a few months. Your water quality entering your RO will at least allow me an educated guess, but it will still only be a guess. The pre and post filters, however, are an entirely different issue and replacement is NOT simply to prevent flow problems. Pre-filters should be replaced at least annually for two reasons. 1) the carbon prefilter will be spent in that period of time, particularly if you are on city water and should be changed to prevent damage to your RO membrane. Additionally, the prefilter is subject to bacterial growth if left too long. The RO filter will remove bacteria, UNLESS it has been damaged. If the RO has been damaged, then the post-filter will be contaminated as well. The ONLY way to know if your RO is still functioning properly is with testing. You can purchase a hand-held TDS meter cheaply. Test before and after RO - TDS should be decreased by 90-99% after the RO. If you don't intend to test, you should replace annually. Guessing is not smart. Assuming your water is "still nice and clean" is not smart. In a nutshell: Replace pre and post filters annually regardless. Either test your water at least annually or replace your RO filter annually. Testing is cheaper and easier.

Way to spam the site @Ryan Stephen. An R/O unit is certainly possible for a small volume drinking water faucet. Other than that, I think you are out of luck. As others have pointed out, what you are suggesting would require the R/O unit to happen ahead of a separate water heater, The entire setup would be crazy expensive, and burn through filters and water. R/O water is aggressive if minerals aren't added back in. It has to be plumbed with plastic pipe. All of the plumbing and fixtures would need to be plastic. So here's a hot tip: I don't think you need a water filter as much as you need a computer filter. Deleting Facebook will remove a whole lot of contaminated thinking around fluoride in your water - not to mention virtually everything else. I'm being dead serious: when you think about actual damage and impact on your health and wellbeing - the misinformation you are getting is far worse than trace amounts of fluoride in your water.

I think a distilled water generating system suitable for all my RO outlets would be impressive, and significantly power hungry. I find "tasteless" RO water very good for making tea; better than just charcoal filtered water with particulate prefilter. However, that test was decades ago, so I can't (and am unlikely to) do a modern direct comparison. My house is prefiltered at 1 micron, and the RO system is further prefiltered with one micron and by charcoal. I was recently wondering about the pore size distribution in the RO filters, so I can't comment on that. Loooong before I would worry about CaCO3 (which I think the water supply puts into the water at somewhat largish sizes, I would worry about ~ 5-10 nm corona virus spike proteins being shed everywhere by a large fraction of the population. Every one of those ingested wants to bind to one of a body cell's ACE2 receptors unless thwarted by enough D3. Normally, RO systems do not remove 100% of the chemicals in the water. In my case, there is enough residual alkalinity to keep the RO water slightly alkaline. This makes it less likely to attack brass in plumbing fixtures. A pure stainless steel fixture should be fine. I don't think most fixture manufacturers will claim to support RO use in general, or RO that they haven't tested, except in the cases where sink fixtures specific to an RO system are supplied. As it happens at my family room "bar" sink, I have a fully brass fixture fed by RO water that I took apart after several years use. I did not see any signs of corrosion.

I know this thread is old, but for others that have the same question... There actually are tankless R.O. systems. Just Google it. Another option for warm climates is to have the tank in the garage versus under the sink. You'd need to run plumbing lines for this during build or remodeling.