The short answer
Both can provide good drinking water. Bottled water is regulated by the FDA and needs no equipment, but it means buying, carrying and discarding containers. A certified under-sink reverse osmosis system treats your own tap water on demand, but it sends some water down the drain and needs regular filter and membrane changes. Which is better depends on your water, your household and your habits.
What each one actually is
Bottled water is a food product regulated by the U.S. Food and Drug Administration. FDA rules set maximum contaminant levels for bottled water, define types such as spring, well and mineral water, and require sanitary bottling practices, including sampling and testing.[source] Some bottled water comes from municipal supplies; it's usually treated, often by distillation or reverse osmosis, before bottling, and water treated that way may be labeled "purified water."[source]
A point-of-use reverse osmosis (RO) system sits under your kitchen sink and treats your own tap water. It uses pressure to force water through a membrane that rejects many contaminants, producing a stream of treated water and a stream of reject water that goes to the drain.[source] Most systems add filters before and after the membrane.[source] Our reverse osmosis page explains the parts.
So in a real sense, you're comparing the same treatment in two places: done at a bottling plant and shipped to you, or done at your sink.
Side by side
| Factor | Under-sink reverse osmosis | Bottled water |
|---|---|---|
| Who checks quality | You, through the product's certification and your own retests. Look for NSF/ANSI 58.[source] | The bottler, under FDA rules and inspections[source] |
| What it removes | Depends on the model's certified claims; RO reduces sodium, dissolved inorganics and many organics[source] | Depends on the source and how it was treated; check the label, and ask the brand for its water quality information |
| Convenience | Water on tap, no carrying or storage | No equipment, works anywhere, but you buy, carry and store it |
| Waste | Sends reject water down the drain; uses replacement cartridges and membranes | Single-use containers (or delivery jugs) to recycle or discard |
| Upkeep | Scheduled filter and membrane changes | Keeping enough on hand |
| Where it fits | Homes that drink and cook with a lot of water | Low use, travel, renters who can't modify plumbing, emergencies |
Water use: the honest downside of RO
Every RO system sends some water to the drain. EPA estimates a typical point-of-use RO system produces at least five gallons of reject water for every gallon of treated water, and some inefficient models use up to ten. Systems with EPA's WaterSense label produce 2.3 gallons or less of reject water per gallon of treated water.[source] If you choose RO, a WaterSense-labeled model is the easy way to cut that down.
Bottled water has its own footprint in packaging and transport, which shows up outside your water bill rather than on it. Neither choice is free of trade-offs.
What RO doesn't do, and when you might not need it
- It removes minerals along with contaminants, including calcium.[source] Some people prefer the taste; some don't.
- It only treats one tap. It's a drinking and cooking solution, not whole-house treatment. Our whole-house vs. point-of-use guide explains the difference.
- It needs maintenance. EPA notes RO membranes and other parts may need replacing over time, and unmaintained systems can make water quality worse.[source] A Care Plan handles the schedule.
- It may be more than you need. If your concern is chlorine taste on city water, a certified carbon filter may be enough. Compare in our whole-home carbon vs. reverse osmosis guide.
Where RO earns its place is when a test shows something worth reducing at the drinking tap, such as arsenic in some private wells or PFAS on some city systems. Our PFAS in Charlotte-area tap water article and drinking-water RO page cover those cases.
Run your own numbers
Cost depends on how much your household drinks, what you pay for bottled water now, and your water rate, so we don't publish a one-size answer. Our RO vs. bottled water calculator lets you enter your own figures and see how they compare over time.
An under-sink RO system connects to your plumbing and drain. Clear Bridge Water supplies and sizes the equipment; here's how licensed installation works.