The pros and cons of reverse osmosis are easy to state and easy to oversell. On the good side, it is the broadest point-of-use treatment a homeowner can buy, and it works on dissolved contaminants that carbon filters barely touch. On the other side, it sends water to drain, it is slow to refill, it takes cabinet space, and it does nothing at all about the hardness scaling your water heater.
The case for it
A membrane rejects dissolved salts, which is a category most household filters cannot address. That makes reverse osmosis the default answer for a household worried about dissolved metals, nitrate or a broad unknown mix, and it is why so many drinking water systems are built around one. It also improves taste noticeably on supplies that taste of minerals or salt, because it takes out the very things doing the tasting.
The costs nobody mentions in the showroom
Some water goes down the drain with every gallon produced, and the ratio worsens as the membrane ages or the feed pressure drops. Refill is slow, so a big pot for pasta empties the tank and you wait. The tank and housings need real cabinet space next to the disposal and the trap. And the system needs cartridge changes on a calendar, because a spent prefilter quietly kills the membrane behind it.
Whole house versus under the sink
Under-sink reverse osmosis treats the water you drink and cook with, which is where contaminant exposure through water mostly happens. Whole-house reverse osmosis is a different animal: it needs pretreatment, a storage tank, a repressurization pump and space, and it is usually chosen for a specific measured problem across every fixture rather than for taste. Treat it as an engineered installation, not a bigger version of the same box.
When it is the wrong buy
If your complaint is scale on the kettle, spots on glassware and stiff laundry, that is hardness and a softener is the tool. If the water runs orange or smells of rotten eggs, you need pretreatment before a membrane, or the membrane fouls. And if the household worry is bacteria on a private well, reverse osmosis is not a disinfection method: that is a testing and disinfection question first.
Questions people ask about pros and cons of reverse osmosis
Does reverse osmosis remove the good minerals too?
Yes, it removes dissolved minerals along with everything else. Many systems offer a remineralization cartridge on the outlet if you want some of them back for taste.
Is the water sent to drain wasted?
It goes to the sewer like any other drain water, and it carries away the rejected salts. Higher feed pressure and a healthy membrane keep that volume lower.
How long does an under-sink reverse osmosis system last?
The housings and tank last many years. The consumables do not: prefilters and postfilters are changed on a schedule and the membrane every few years.